A/D converter circuit and semiconductor integrated circuit

ABSTRACT

An analog-to-digital converter circuit having a simple design and capable of preventing an increase in surface area and other problems. An analog-to-digital converter circuit for converting an analog input signal to a digital quantity includes an analog-to-digital converter unit that converts analog input signals to pre-correction digital values, and a corrector unit that digitally corrects the pre-connection digital values output from the analog-to-digital converter unit. The corrector unit includes a weighting coefficient multiplier unit that outputs a post-correction digital value obtained by multiplying the weighting coefficients provided for each bit by each bit of the pre-correction digital value output from the A/D converter unit and summing them, and a weighting coefficient search unit that searches for weighting coefficients so as to minimize an error signal generated based on the post-correction digital value and an approximate value for the post-correction digital value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2013-272727 filed onDec. 27, 2013 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

The present invention relates to an analog/digital (A/D) convertercircuit for converting an analog quantity to a digital quantity.

BACKGROUND

Sequential comparison ADC (Analog to Digital Converter) is one type ofA/D (analog/digital) conversion system. High-speed and high-accuracy AD(analog to digital) conversion has become possible by way of CMOSprocess miniaturization so that sequential comparison ADC is nowutilized in a wide range of fields from conventional sensor applicationsto wireless communications, etc. Among these fields, sequentialcomparison ADC that performs non-binary conversion has, provenparticularly resistant (robust) to unwanted effects such as devicemismatches caused by process miniaturization and so research in thisarea has been reported in academic conferences in recent years.

In binary sequential comparison ADC of the related art is based onbinary search, digital values are decided by a binary search performedin order from high-order bits while applying feedback to the analogsignal that is input in the DAC (Digital to Analog Converter). Theweight of each bit is therefore applied at a power of 2. In other words,the relation between the digital output value x and each bit D_(i) fromthe AD conversion results is given by the following formula.

$\begin{matrix}{x = {\sum\limits_{i = 0}^{N - 1}{2^{i}D_{i}}}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

In some cases, D_(i)={0,1} and D_(i)={−1, +1} according to the notationmethod but are still essentially the same. Unless stated to thecontrary, the notation D_(i) {−1, +1} is utilized here.

In non-binary ADC however the weight of each bit is given by ADC that isnot a power of 2. Namely, in non-binary ADC, the relation between thedigital output x and each bit Di in the AD conversion results is givenin the following formula.

$\begin{matrix}{x = {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}}}} & \lbrack {{Formula}\mspace{14mu} 2} \rbrack\end{matrix}$

Here, W_(i) is the weighting coefficient and is typically a valuediffering from 2^(i). The non-binary ADC can usually be configured byselecting W_(i+1)/W_(i)<2 so that there are plural AD conversion resultsrelative to the analog value. The presence of plural AD conversionresults in other words signifies that there are plural search routes,forming this type of structure allows redundancy in the conversions.

Correct AD conversion results can therefore be obtained due toredundancy even if a conversion error occurs in the process forsequential comparison due to noise in the comparator or an incompletesetting for feedback DAC.

However in non-binary ADC, unless the coefficient of the feedback DACmatches the value of the weighted coefficient W_(i), the AD conversionaccuracy will deteriorate due to errors occurring in the digital outputvalue.

A weighting coefficient W_(i) must be accurately calculated in order toperform accurate AD conversion to cope with fluctuation in the feedbackDAC coefficient relative to the design value due to productionvariations, power supply voltage, and operating temperature, etc. Inparticular, in order to maintain an optimum value for the weightingcoefficient W_(i) for coping with fluctuations during circuit usage suchas the power supply voltage, and operating temperature, the search forthe weighting coefficient must be performed in parallel with circuitoperation or in other words, a background operation is required.

To meet this need, a method utilizing the LMS (Least-Mean-Square)algorithm is known as a method to find the weighting coefficient of thenon-binary ADC. The LMS algorithm is a calculation method that is onetype of so-called adaptive algorithm that generates an error signal andsets a weighting coefficient so that the generated error signalapproaches zero.

The non-patent documents 1 through 4 each disclose an A/D convertercircuit that applies the LMS algorithm. The A/D converter circuit iscomprised of an A/D converter unit to convert the analog input signalsinto digital values, and a corrector unit to digitally correct theoutput of the A/D converter unit. These non-patent documents 1 through 4propose a low power consumption, and high-speed and high-accuracy A/Dconverter circuit that performs digital correction by applying a LMSalgorithm in the corrector unit.

[Non-Patent Document 1]

T. Oshima, et al., “Fast nonlineardeterministic calibration of pipelinedA/D converters,” IEEE 2008 Midwest Symposiumon Circuits and Systems,Session C2L-C-1, August 2008.

[Non-patent document 2]

T. Oshima, et al., “23-mW 50-MS/s10-bit pipeline A/D converter withnonlinear LMS foreground calibration,” 2009 International Symposium onCircuits and Systems, pp. 960-963, May 2009.

[Non-Patent Document 3]

J. Mcneill, et al., “A split-ADC architecture for deterministic digitalbackground calibration of a 16b 1MS/s ADC,” IEEE2005 InternationalSolid-State Circuits Conference, pp. 276-277, February 2005.

[Non-Patent Document 4]

W. Liu et al., “A 12b 22.5/45MS/s3.0 mW 0.059 mm² CMOS SAR ADC achievingover 90 dB SFDR,” IEEE 2010 International Solid-State CircuitsConference, pp. 380-381, February 2010.

SUMMARY

The A/D converter circuits shown in non-patent documents 1 through 3 onthe other hand, are comprised of plural A/D converter units that lead tothe problems of a larger surface area and larger current consumption.

The A/D converter circuits in non-patent document 4 require a mechanismto apply an offset, and this mechanism also leads to the problems of alarger surface area and larger current consumption as well as anincrease in the design man-hours.

In order to resolve the aforementioned problems, the present inventionhas the object of providing an A/D converter circuit and a semiconductorintegrated circuit capable of preventing an increase in the surface areaand other problems by utilizing a simple structure.

The novel features and other issues of the present invention will becomereadily apparent from the description in the present specifications andthe accompanying drawings.

According to one aspect of the present invention, an A/D convertercircuit for converting an analog input signal into a digital quantityincludes an A/D converter unit that converts the analog input signalinto a pre-correction digital value, and a corrector unit that digitallycorrects the pre-correction digital value output from the A/D converterunit. The corrector unit includes a weighting coefficient multiplierunit that outputs a post-correction digital value obtained by summingthe weighting coefficients provided in each bit multiplied by thepre-correction digital value of each bit output from the A/D converterunit; and a weighting coefficient search unit that searches forweighting coefficients so as to minimize an error signal generated basedon the post-correction digital value and an approximate value for thepost-correction digital value.

According to one aspect of the present invention, the above structure iscapable of preventing an increase in the surface area and otherdisadvantages by utilizing a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit basedon the first embodiment;

FIG. 2 is, a drawing for describing the concept of searching weightingcoefficients in the A/D converter circuit based on the first embodiment;

FIG. 3 is a drawing for describing the converging of the error signalsin the A/D converter circuit based on the first embodiment;

FIGS. 4A and 4B are drawings for describing specific examples of thefrequency spectrum output by the A/D converter circuit based on thefirst embodiment;

FIG. 5 is a block diagram for describing the function of a search vectorgenerator unit and an error signal generator unit based on the firstembodiment;

FIG. 6 is a drawing for describing the circuit structure of the A/Dconverter circuit based on the first embodiment;

FIG. 7 is a drawing for describing the calculation of the estimationvalue ξ(k) by four-point interpolation based on the first embodiment;

FIG. 8 is a drawing for describing the circuit structure of A/Dconverter circuit based on the first embodiment;

FIG. 9 is a drawing for describing the circuit structure of A/Dconverter circuit based on the first embodiment;

FIG. 10 is a drawing for describing the circuit structure of A/Dconverter circuit based on a first modification of the first embodiment;

FIG. 11 is an outline diagram for describing the structure of A/Dconverter circuit based on a second modification of the firstembodiment;

FIG. 12 is a drawing for describing the circuit structure of A/Dconverter circuit based on a second modification of the firstembodiment;

FIG. 13 is an outline diagram for describing the structure of A/Dconverter circuit based on a third modification of the first embodiment;

FIG. 14 is a drawing for describing the circuit structure of A/Dconverter circuit based on a third modification of the first embodiment;

FIG. 15 is a drawing for describing the circuit structure of the IIRfilter based on a third modification of the first embodiment;

FIG. 16 is an outline diagram for describing the structure of the A/Dconverter circuit based on a fourth modification of the firstembodiment;

FIG. 17A and FIG. 17B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit basedon the second embodiment;

FIG. 18A and FIG. 18B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit basedon the second embodiment;

FIG. 19A and FIG. 19B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit basedon the second embodiment;

FIG. 20 is an outline diagram for describing the structure of the A/Dconverter circuit based on a first modification of the secondembodiment;

FIG. 21 is an outline diagram for describing the structure of the A/Dconverter circuit based on a first modification of the secondembodiment;

FIG. 22 is a drawing for describing the structure of the A/D convertercircuit based on a first modification of the second embodiment;

FIG. 23 is a drawing for describing the A/D converter circuit 3 based ona second modification of the second embodiment;

FIG. 24 is a drawing for describing the A/D converter circuit based on asecond modification of the second embodiment;

FIG. 25 is a drawing for describing the A/D converter circuit based on asecond modification of the second embodiment;

FIG. 26A and FIG. 26B are drawings for describing the signal input tothe A/D converter unit based on the third embodiment;

FIG. 27 is a circuit structure diagram of a test signal generatorcircuit based on the third embodiment;

FIG. 28 is an outline diagram for describing the structure of the A/Dconverter circuit based on the fourth embodiment;

FIG. 29A and FIG. 29B are drawings for describing the converging of theerror signals based on the fourth embodiment;

FIG. 30 is a drawing for describing the structure of a wireless receiverbased on the fifth embodiment;

FIG. 31 is a drawing for describing a sensor based on a modification ofthe fifth embodiment;

FIG. 32 is a drawing for describing the structure of the AFE124 based ona modification of the fifth embodiment;

FIG. 33 is an outline diagram for describing the structure of the A/Dconverter circuit based on the sixth embodiment;

FIG. 34 is an outline diagram for describing the structure of the A/Dconverter circuit based on the sixth embodiment;

FIG. 35A and FIG. 35B are outline diagrams for describing the structureof the A/D converter circuit and a coefficient search unit based on amodification of the sixth embodiment; and

FIG. 36A and FIG. 36B are outline diagrams for describing the structureof the A/D converter circuit and a coefficient search unit based on amodification of the sixth embodiment.

DETAILED DESCRIPTION

The embodiments are described in detail next while referring to thedrawings. In the drawings, the same reference symbols and referencenumerals express identical or equivalent sections and redundantdescriptions are omitted.

First Embodiment Structure of the Analog/Digital (A/D) Converter Circuit

FIGS. 1A and 1B are an outline diagram and a conversion timing drawingof the A/D converter circuit 1 based on the first embodiment.

In this example, the A/D converter circuit 1 for converting the analoginput signal into a digital quantity is described while referring toFIG. 1A.

The A/D converter circuit 1 contains an A/D converter unit (ADC) 10, asearch vector generator unit 20, a digital corrector unit 30, an errorsignal generator unit 40, and a coefficient search unit 50.

The A/D converter unit 10 converts an analog input signal into a digitalvalue representing the AD conversion results. The search vectorgenerator unit 20 calculates a search vectorδ_(i) ^((k)) based on theapproximate value of each bit D_(i) ^((k)) for each bit D_(i) ^((k)) ofthe digital value output from the A/D converter unit 10. In the presentexample, the search vector generator unit 20 calculates theinterpolation bit estimation value based on the approximate value ofeach bit D_(i) ^((k)) and calculates the search vector δ_(i) ^((k)) onthe difference between each bit D_(i) ^((k)) and the interpolation bitestimation value.

The error signal generator unit 40 calculates an error signal e(k) basedon the digital value x(k) output from the digital corrector unit 30, andthe approximate value. In the present example, the error signalgenerator unit 40 calculates an error signal e(k) based on error signalinterpolation estimation value based on x(k) the approximate value, andthe digital value.

The coefficient search unit 50 searches for a weighting coefficient soas to minimize the error signal generated based on the digital valuex(k) output from the digital corrector unit 30, and the approximatevalue. Specifically, the coefficient search unit 50 searches for aweighting coefficient W_(i) for each bit based on the error signal e(k)output from the error signal generator unit 40 and the search vectorδ_(i) ^((k)) output from the search vector generator unit 20. In thepresent example, the coefficient search unit 50 rewrites the weightingcoefficient W_(i) for each bit by multiplying the error signal e(k), andthe search vector δ_(i) ^((k)) utilized for searching the weightingcoefficient W_(i) generated based on each bit D_(i) ^((k)) the digitalvalue output from the corresponding A/D converter unit 10, and theapproximate value for each, bit D_(i) ^((k)) and summing them.

The digital corrector unit 30 digitally corrects of each bit D_(i)^((k)) of the digital value output from the A/D converter unit 10according to the weighting coefficient W_(i) of each bit searched by thecoefficient search unit 50. Specifically, the digital corrector unit 30calculates the digital value x(k) by multiplying the weightingcoefficient W_(i) by each bit D_(i) ^((k)) of the digital value from theA/D converter unit 10 and summing them.

In the present example, the digital value output from the A/D converterunit 10 is called the pre-correction digital value, and the digitalvalue output from the digital corrector unit 30 is called thepost-correction digital value.

An outline diagram of the conversion timing by the A/D converter circuit1 is shown here while referring to FIG. 1B. The present example showsthe case where repeatedly and alternately executing the sampling (“S”)as one example of sampling processing of the analog input signal, andthe AD conversion (“AD”) for processing the sampled analog input signalby A/D conversion. The sampling may utilize a structure contained in theA/D converter unit 10 or a structure contained in a pre-stage of the A/Dconverter unit 10.

FIG. 2 is a drawing for describing the concept of searching weightingcoefficients in the A/D converter circuit 1 based on the firstembodiment.

Referring now to FIG. 2, the coefficient search unit 50 searches theweighting coefficients by utilizing an optimization algorithm (LMS{least-mean-square} algorithm and so on) so as to minimize thedifference between the digitally corrected post-correction digital valueand the interpolation estimation value based on the approximate valuefor the post-correction digital value.

The present example describes two point interpolation which ispolynomial interpolation as one example of interpolation however thereare no particular restrictions on the interpolation method to beutilized and linear interpolation, Lagrange interpolation, Newtoninterpolation and spline interpolation as well as others may beutilized. The specific example of an interpolation method given for thepresent embodiment is linear interpolation but other types ofinterpolation method may also be utilized.

In the present example utilizing an LMS algorithm is described as theoptimization algorithm however there are no particular restrictions onthe algorithm for utilization and the learning identification method,projection method, conjugate gradient method, RLS (Recursive LeastSquare) algorithm, BLMS (Block least-mean-square) algorithm, and jumpalgorithm and so on may be utilized.

The A/D converter unit 10, the digital corrector unit 30, the searchvector generator unit 20, the error signal generator unit 40, and thecoefficient search unit 50 may be formed on the same chip or may beformed on respectively different chips. Moreover, the digital correctorunit 30, the search vector generator unit 20, the error signal generatorunit 40, and the coefficient search unit 50 are for digital signalprocessing and so may be achieved through hardware processing in logiccircuits or may be achieved through software processing on computers.

The present example describes the case where searching for weightingcoefficients by way of an optimization algorithm so as to minimize theerror signal which is the difference between the digitally correctedpost-correction digital value and the interpolation estimation valuebased on the approximate value for the post-correction digital value.However, the method is not limited to an error signal versus theinterpolation estimation value and any method may be utilized as longprovided the method searches for a weighting coefficient so as tominimize the error signal based on the post-correction digital value andthe approximate value for the post-correction digital value.

The present example mainly describes applying sequential comparison ADC,pipeline ADC, cyclic ADC as the ADC method however there are noparticular restrictions on the ADC method and other ADC methods such asflash ADC may also be utilized.

FIG. 3 is a drawing for describing the converging of the error signalsin the A/D converter circuit 1 based on the first embodiment.

Referring to FIG. 3, the A/D converter circuit 1 based on the firstembodiment is capable of checking the error signal convergence byrepeating the search processing for the target weighting coefficient,and in the present example by repeating the search processing about1,000 times as one example.

FIG. 4A and FIG. 4B are drawings for describing specific examples of thefrequency spectrum of the output by the A/D converter circuit 1 based onthe first embodiment.

The present example shows the frequency spectrum of the output whensampling a sine wave of a 225 KHz analog input signal at a samplingfrequency of 10 MHz in the A/D converter circuit 1.

FIG. 4A is the frequency spectrum prior to searching for the weightingcoefficient.

FIG. 4B is the frequency spectrum after searching for the weightingcoefficient.

Results from optimizing the weighting coefficient by searching for thetarget weighting coefficient confirm that the high frequencies (RF) andnoise floor are reduced in the frequency spectrum. The SNDR(Signal-to-noise and distortion ratio) are at this time improved from44.5 dB to 75.7 dB. Moreover, the ENOB (Effective Number Of Bits) isimproved from 7.10 bits to 12.28 bits. The ENOB is calculated by finding(SNDR−1.76)/6.02.

A specific example of interpolation is described next.

(Specific Example of Two Point Interpolation)

The weighting coefficient search method utilizing two-pointinterpolation as polynomial interpolation, and an LMS algorithm as theoptimizing algorithm is described next.

The weighting coefficient search formula utilizing two-pointinterpolation is expressed in the next formula as follows.[Formula 3]W _(i) ^((new)) =W _(i) ^((old))−μ_(i)′[2x(k−1)−x(k)+x(k−2)]×(2D _(i)^((k-1)) −D _(i) ^((k)) +D _(i) ^((k-2)))  (1)

The meaning of each variable is given here as follows:

W_(i) ^((new)): Weighting coefficient after rewrite (post-rewriteweighting coefficient W_(i) ^((old)))

W_(i) ^((old)): Weighting coefficient before rewrite (pre-rewriteweighting coefficient W_(i) ^((old)))

μ_(i)′: Appropriate constant. Controls convergence speed of thecoefficient search

k: Index expressing the No. of the sample.

x(k): Digital output value obtained by AD converting the k-th sample

D_(i) ^((k)):i-th bit of AD conversion result for k-th sample

The formula (1) is derived as follows.

The output value x(k) for the A/D converter unit 10 is first of allexpressed in the following formula (2).

$\begin{matrix}\lbrack {{Formula}\mspace{14mu} 4} \rbrack & \; \\{{x(k)} = {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}}} & (2)\end{matrix}$

The estimation value ξ(k) found from two-point interpolation of x(k) isan average value for x(k+1) and x(k−1) so ξ(k) is given by the followingformula (3).

$\begin{matrix}{{\xi(k)} = {{\frac{1}{2}\lbrack {{x( {k + 1} )} + {x( {k - 1} )}} \rbrack} = {\frac{1}{2}( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 1})}}} + {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 1})}}}} )}}} & (3)\end{matrix}$

Therefore, the error e(k) for the estimation value ξ(k) and ADconversion value x(k) from formula (2) and formula (3) is as follows.

$\begin{matrix}\begin{matrix}{{e(k)} = {{{x(k)} - {\xi(k)}} = {{x(k)} - {\frac{1}{2}\lbrack {{x( {k + 1} )} + {x( {k - 1} )}} \rbrack}}}} \\{= {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}} - {\frac{1}{2}( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 1})}}} + {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 1})}}}} )}}} \\{= {\sum\limits_{i = 0}^{N - 1}{W_{i}( {D_{i}^{(k)} - {\frac{1}{2}D_{i}^{({k + 1})}} - {\frac{1}{2}D_{i}^{({k - 1})}}} )}}}\end{matrix} & (4)\end{matrix}$

The search vector δ_(i) ^((k)) is:

$\begin{matrix}{\delta_{i}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{i}} = {D_{i}^{(k)} - {\frac{1}{2}D_{i}^{({k + 1})}} - {\frac{1}{2}D_{i}^{({k - 1})}}}}} & ( {4A} )\end{matrix}$

On the other hand the formula for searching the weighting coefficientwhen the LMS algorithm is applied so as to minimize e(k) is given asfollows:

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {\mu_{i}{e(k)}\frac{\partial{e(k)}}{\partial W_{i}}}}} & (5)\end{matrix}$

So that from applying formula (A) and formula (5):

$\begin{matrix}\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {\mu_{i}{e(k)}( {D_{i}^{(k)} - {\frac{1}{2}D_{i}^{({k + 1})}} - {\frac{1}{2}D_{i}^{({k - 1})}}} )}}} \\{= {W_{i}^{({old})} - {{\mu_{i}\lbrack {{x(k)} - {\frac{1}{2}{x( {k + 1} )}} - {\frac{1}{2}{x( {k - 1} )}}} \rbrack} \times}}} \\{( {D_{i}^{(k)} - {\frac{1}{2}D_{i}^{({k + 1})}} - {\frac{1}{2}D_{i}^{({k - 1})}}} )}\end{matrix} & (6)\end{matrix}$

Here, μ_(i)=4μ_(i)′ and by substituting k→k−1, and interchanging thesequence of the terms, the following formula (7) is obtained.

$\begin{matrix}\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}^{\prime}\lbrack {{x(k)} - {2\;{x( {k - 1} )}} + {x( {k - 2} )}} \rbrack} \times}}} \\{( {D_{i}^{(k)} - {2\; D_{i}^{({k - 1})}} + D_{i}^{({k - 2})}} )} \\{= {W_{i}^{({old})} - {{\mu_{i}^{\prime}\lbrack {{2\;{x( {k - 1} )}} - {x(k)} - {x( {k - 2} )}} \rbrack} \times}}} \\{( {{2\; D_{i}^{({k - 1})}} - D_{i}^{(k)} + D_{i}^{({k - 2})}} )}\end{matrix} & (7)\end{matrix}$

Formula (1) is calculated as described above.

FIG. 1 can be functionally executed as shown next in compliance withformula (1).

FIG. 5 is a block diagram for describing the function of the searchvector generator unit 20 and error signal generator unit 40 the based onthe first embodiment.

The search vector generator unit 20 as shown in FIG. 5, includes a delayunit 22, a subtracter 24, and an interpolation bit estimation valuecalculation unit 26.

The interpolation bit estimation value output unit 26 calculates theinterpolation bit estimation value based on the approximate value ofeach bit in the pre-correction digital value.

The delay unit 22 uses the subtracter 24 to adjust the timing forobtaining the difference between each bit of the pre-correction digitalvalue, and the interpolation bit estimation value from the interpolationbit estimation value calculation unit 26.

The subtracter 24 outputs the search vector δ_(i) ^((k)) for each bitbased on the difference between each bit of the pre-correction digitalvalue and the interpolation bit estimation value from the interpolationbit estimation value calculation unit 26.

The error signal generator unit 40 is comprised of the delay unit 42,the subtracter 44, and the interpolation estimation value calculationunit 46.

The interpolation estimation value calculation unit 46 calculates theinterpolation estimation value based on the approximate value of thepost-correction digital value x(k).

The delay unit 42 uses the subtracter 44 to adjust the timing whenobtaining the difference between interpolation estimation value from theinterpolation estimation value calculation unit 46, and thepost-correction digital value.

The subtracter 44 outputs the error signal e(k) based on the differencebetween the post-correction digital value, and the interpolationestimation value output from the interpolation estimation valuecalculation unit 46.

FIG. 6 is a drawing for describing the circuit structure of the A/Dconverter circuit 1 based on the first embodiment.

The A/D converter circuit 1 shown in FIG. 6 is configured as shown inthe drawing in compliance with “2D_(i) ^((k-1))−D_(i) ^((k))−D_(i)^((k-2))” of formula 1. More specifically, the search vector generatorunit 20 is comprised of the delay elements 200, 202, the multipliers204, 206, 208, and the adder 210. The A/D converter circuit 1 in thisway calculates the search vector δ_(i) ^((k)) corresponding to each bit.

The error signal generator unit 40 is configured as shown in the drawingin compliance with “2x(k−1)−x(k)−x(k−2)” of formula 1. Morespecifically, the error signal generator unit 40 is comprised of thedelay elements 400, 402, the multipliers 404, 406, 408, and the adder410. The error signal generator unit 40 in this way calculates the errorsignal e(k) which is the difference between the post-correction digitalvalue and the interpolation estimation value based on the approximatevalue of the post-correction digital value.

The coefficient search unit 50 is comprised of a multiplier 52 for themultiplying factor μ_(i)′ according to formula (1), a multiplier 54 formultiplying the output of the multiplier 52 with the error signal e(k),a subtracter 56 to subtract the output from the multiplier 54 from thepre-rewrite weighting coefficient W_(i) ^((old)), and a retention unit58 to output the output from the subtracter 56 as the post-rewriteweighting coefficient W_(i) ^((new)).

The digital corrector unit 30 is comprised of a multiplier 32 tomultiply the post-correction weighting coefficient W_(i) ^((new)) by thepre-correction digital value for each bit, and the integrator 34 tooutput the post-corrected digital value x(k) that is integrated from thevalue f each bit multiplied in the multiplier 32.

The above structure or in other words, the error signal generator unit40 calculates the error signal e(k) which is the difference between thepost-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value. Thesearch vector generator unit 20 then calculates the interpolation bitestimation value based on the approximate value of each bit D_(i) ^((k))for the digital value each bit D_(i) ^((k)) and calculates the searchvector δ_(i) ^((k)) based on that difference.

The correction direction for the weighting coefficient, of each bit isdetermined by the search vector δ_(i) ^((k)), and the weightingcoefficient can be converged to an optimum value so as to reduce theerror signal e(k) by the coefficient search unit 50 by utilizing the LMSalgorithm.

The A/D converter circuit 1 can therefore execute high-speed andhigh-accurate A/D conversion processing based on the first embodiment.

In comparison with the example of the related art, the structure ornamely the AD converter circuit 1 based on the first embodiment is asimple structure including a single A/D converter unit (ADC), andfurther requires no mechanism for applying an offset so that along witha smaller surface area, an increase in consumption current can also beprevented.

(Specific Example of 4-Point Interpolation)

A search method for weighting coefficients utilizing 4-pointinterpolation as polynomial interpolation is described.

A weighting coefficient search formula utilizing 4-point interpolationis shown in the next formula.[Formula 5]W _(i) ^((new)) =W _(i) ^((old))−μ_(i)′[x(k)−4x(k−1)+6x(k−2)−4x(k−3)+x(k−4)]×(D _(i) ^((k))−4D _(i)^((k-1))+6D _(i) ^((k-2))−4D _(i) ^((k-3)) +D _(i) ^((k-4)))  (3)

Formula (8) is derived as follows.

The digital output value x(k) for the A/D converter unit 10 is expressedin the formula (2) as described for 2-point interpolation.

[Formula 6]

The estimation value ξ(k) found from four-point interpolation of x(k) isgiven by the following formula (9) utilizing formula (14).

$\begin{matrix}\begin{matrix}{{\xi(k)} = {\frac{1}{6}\lbrack {{4\;{x( {k + 1} )}} + {4\;{x( {k - 1} )}} - {x( {k + 2} )} - {x( {k - 2} )}} \rbrack}} \\{= {\frac{1}{6}( {{4{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 1})}}}} + {4{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 1})}}}} - {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 2})}}} + {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 2})}}}} )}}\end{matrix} & (9)\end{matrix}$

Therefore, the error e(k) for the AD conversion value x(k) andestimation value ξ(k) are given as follows from formula (2) and formula(9).

$\begin{matrix}\begin{matrix}{{e(k)} = {{x(k)} - {\xi(k)}}} \\{= {{x(k)} - {\frac{1}{6}\lbrack {{4\;{x( {k + 1} )}} + {4\;{x( {k - 1} )}} - {x( {k + 2} )} - {x( {k - 2} )}} \rbrack}}} \\{= {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}} - {\frac{1}{6}( {{4\;{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 1})}}}} + {4{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 1})}}}} -} }}} \\ {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k + 2})}}} + {\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - 2})}}}} ) \\{= {\sum\limits_{i = 0}^{N - 1}{W_{i}( {D_{i}^{(k)} - {\frac{2}{3}D_{i}^{({k + 1})}} - {\frac{2}{3}D_{i}^{({k - 1})}} + {\frac{1}{6}D_{i}^{({k + 2})}} + {\frac{1}{6}D_{i}^{({k - 2})}}} )}}}\end{matrix} & (10)\end{matrix}$The search vector δ_(i) ^((k)) is found by:

$\begin{matrix}{\delta_{i}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{i}} = {D_{i}^{(k)} - {\frac{2}{3}D_{i}^{({k + 1})}} - {\frac{2}{3}D_{i}^{({k - 1})}} + {\frac{1}{6}D_{i}^{({k + 2})}} - {\frac{1}{6}D_{i}^{({k - 2})}}}}} & ( {10A} )\end{matrix}$

On the other hand, the search formula for the weighting coefficient whenan LMS algorithm is applied so as to minimize e(k) is given as follows:

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {\mu_{i}{e(k)}\frac{\partial{e(k)}}{\partial W_{i}}}}} & (11)\end{matrix}$So that from formula (10A) and formula (11) we obtain

$\begin{matrix}\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {\mu_{i}{e(k)}( {D_{i}^{(k)} - {\frac{2}{3}D_{i}^{({k + 1})}} - {\frac{2}{3}D_{i}^{({k - 1})}} +} }}} \\ {{\frac{1}{6}D_{i}^{({k + 2})}} + {\frac{1}{6}D_{i}^{({k - 2})}}} ) \\{= {W_{i}^{({old})} - {\mu_{i}\lbrack {{x(k)} - {\frac{2}{3}{x( {k + 1} )}} - {\frac{2}{3}{x( {k - 1} )}} +} }}} \\{ {{\frac{1}{6}{x( {k + 2} )}} + {\frac{1}{6}{x( {k - 2} )}}} \rbrack \times} \\{( {D_{i}^{(k)} - {\frac{2}{3}D_{i}^{({k + 1})}} - {\frac{2}{3}D_{i}^{({k - 1})}} + {\frac{1}{6}D_{i}^{({k + 2})}} + {\frac{1}{6}D_{i}^{({k - 2})}}} )}\end{matrix} & (12)\end{matrix}$

Here, with μ_(i)′=36μ_(i)′, and substituting k→k−2, and interchangingthe sequence of the terms gives the following formula (13).W _(i) ^((new)) =W _(i) ^((old))−μ_(i)′[x(k)−4x(k−1)+6x(k−2)−4x(k−3)+x(k−4)]×(D _(i) ^((k))−4D _(i)^((k-1))+6D _(i) ^((k-2))−4D _(i) ^((k-3)) +D _(i) ^((k-4)))  (13)

The above allows calculating the formula (8).

Here the calculation of the estimation value ξ(k) by 4-pointinterpolation is described while referring to FIG. 7.[Formula 7]ξ(k)=1/6[4x(k+1)+4x(k−1)−x(k+2)−x(k−2)]  (14)

The AD conversion value first of all approximates the cubic curve in thefollowing formula (15).ξ(t)=a(t−k)³ +b(t−k)² +c(t−k)+d  (15)

Assuming that each point (k−2, k−1, k+1, k+2) on this approximate curvematches the AD conversion values, then the following is obtained:x(k−2)=ξ(k−2)=−8a+4b−2c+d  (16)x(k−1)=ξ(k−1)=−a+b−c+d  (17)x(k+1)=ξ(k+1)=a+b+c+d  (18)x(k+2)=ξ(k+2)=8a+4b+2c+d  (19)

The estimation value ξ(k) on the other hand is given by the followingformulaξ(k)=d  (20)

The intermediate points η(1), η(2) are defined in the followingformulas.

$\begin{matrix}{{\eta(1)} = {\frac{{x( {k + 1} )} + {x( {k - 1} )}}{2} = {b + d}}} & (21) \\{{\eta(2)} = {\frac{{x( {k + 2} )} + {x( {k - 2} )}}{2} = {{4\; b} + d}}} & (22)\end{matrix}$

Here, eliminating b gives:4η(1)−η(2)=3d  (23)

so therefore, solving for d yields:ξ(k)=d=1/3(4η(1)−η(2))=1/6[4x(k+1)+4x(k−1)−x(k+2)−k−2)]  (24)

FIG. 8 is a drawing for describing the circuit structure of A/Dconverter circuit 1# based on the first embodiment. The A/D convertercircuit 1# shown in FIG. 8, searches for a weighting coefficient byutilizing 4-point interpolation. In the present example, along withsubstituting the search vector generator unit 20 described in FIG. 4,with the search vector generator unit 20#, the error signal generatorunit 40 is substituted with the error signal generator unit 40#. Theother structural elements are identical so a redundant description isomitted.

More specifically, the search vector generator unit 20# is configured asshown in the drawing according to “D_(i) ^((k))−4D_(i) ^((k-1))+6D_(i)^((k-2))−4D_(i) ^((k-3))+D_(i) ^((k-4))” in formula (8). Specifically,the search vector generator unit 20 is comprised of the delay elements220 to 226, the multipliers 228 to 236, and the adder 238. A searchvector δ_(i) ^((k)) corresponding to each bit can in this way becalculated.

The error signal generator unit 40# is comprised as shown in the drawingaccording to “x(k)−4x(k−1)+6x(k−2)−4x(k−3)+x(k−4)” in formula (8).Specifically, the error signal generator unit 40# is comprised of thedelay elements 420 to 426, the multipliers 428 to 436, and the adder438. The error signal e(k) which is the difference between thepost-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value iscalculated in this way.

The coefficient search unit 50 according to the formula (8) is comprisedof a multiplier 52 having a multiplying factor μ_(i)′, a multiplier 54for multiplying the output of the multiplier 52 and the error signale(k), a subtracter 56 for subtracting the output from the multiplier 54from the pre-rewrite weighting coefficient W_(i) ^((old)), and retentionunit 58 to output the output from the subtracter 56 as the post-rewriteweighting coefficient W_(i) ^((new)).

The digital corrector unit 30 is comprised of a multiplier 32 tomultiply the post-rewrite weighting coefficient W_(i) ^((new)) by thepre-correction digital value for each bit, and the integrator 34 tooutput the post-corrected digital value x(k) which is integrated fromthe value of each bit multiplied in the multiplier 32.

The above structure or in other words, the error signal generator unit40# calculates the error signal e(k) which is the difference between thepost-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value. Thesearch vector generator unit 20# then calculates the interpolation bitestimation value based on the approximate value of each bit D_(i) ^((k))for each bit D_(i) ^((k)) of the digital value and calculates the searchvector δ_(i) ^((k)) based on that difference.

The correction direction for the weighting coefficient of each bit isdetermined by the search vector δ_(i) ^((k)), and the weightingcoefficient can be converged to an optimum value so as to reduce theerror signal e(k) by the coefficient search unit 50 by utilizing the LMSalgorithm.

The A/D converter circuit 1# based on the first embodiment can thereforeexecute high-speed and high-accurate A/D conversion processing.

In comparison to the example of the related art, the above structure ornamely the AD converter circuit 1# based on the first embodiment has asimple structure including a single A/D converter unit (ADC), and alsorequiring no mechanism for applying an offset so that along with asmaller surface area, an increase in current consumption can also beprevented.

(Specific Example of 2n-Point Interpolation)

[Formula 8]

In the weighting coefficient formulas (1) and (8) for 2-point and4-point interpolation, the coefficient for each term in the formula forthe error signal is a binomial coefficient. In other words, in the caseof 2-point interpolation the coefficient is (1 −2 1)=(₂C₂ −₂C₁ ₂C₀); andin the case of 4-point interpolation the coefficient is (1 −4 6 −41)=(₄C₄ −₄C₃ ₄C₂ −₄C₁ ₄C₀). The approach is generally the same for2-point interpolation so each coefficient becomes (−1)^(n-1) _(n)C₁. Theweighting coefficient is therefore as shown below.

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}^{\prime}\lbrack {\sum\limits_{l = 0}^{2\; n}{( {- 1} )_{n}^{n - 1}C_{l}{x( {k - l} )}}} \rbrack} \times \lbrack {\sum\limits_{l = 0}^{2\; n}{( {- 1} )_{n}^{n - 1}C_{l}D_{i}^{({k - l})}}} \rbrack}}} & (25)\end{matrix}$

FIG. 9 is a drawing for describing the circuit structure of A/Dconverter circuit 1#A based on the first embodiment.

The A/D converter circuit 1#A shown in FIG. 9, searches for a weightingcoefficient by utilizing 2n-point interpolation. In the present example,along with substituting the search vector generator unit 20 described inFIG. 4, with the search vector generator unit 20#A, the error signalgenerator unit 40 is substituted with the error signal generator unit40#A. The other elements are identical so a redundant description isomitted.

More specifically, the search vector generator unit 20# is configured asshown in the drawing according to formula (25). Specifically, the searchvector generator unit 20# is comprised of the delay elements 200A1 to200An, the multipliers 200B1 to 200B (n+1), and the adder 200C. A searchvector δ_(i) ^((k)) corresponding to each bit is calculated in this way.

The error signal generator unit 40#A is comprised as shown in thedrawing according to the formula (25) described above. Morespecifically, the error signal generator unit 40#A is comprised of thedelay elements 400A1 to 400An, the multipliers 400B1 to 400B (n+1), andthe adder 400C. The error signal e(k) which is the difference betweenthe post-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value iscalculated in this way.

The coefficient search unit 50 according to the formula (25) iscomprised of a multiplier 52 having a the multiplying factor μ′_(i), amultiplier 54 for multiplying the output of the multiplier 52 and theerror signal e(k), a subtracter 56 for subtracting the output from themultiplier 54 from the pre-rewrite weighting coefficient W_(i) ^((old))and a retention unit 58 to output the output from the subtracter 56 asthe post-rewrite weighting coefficient W_(i) ^((new)).

The digital corrector unit 30 is comprised of a multiplier 32 tomultiply the post-correction weighting coefficient W_(i) ^((new)) byeach bit of the pre-correction digital value, and the integrator 34 tooutput the post-correction digital value x(k) which is integrated fromthe value of each bit that is multiplied in the multiplier 32.

The above structure or in other words, the error signal generator unit40#A calculates the error signal e(k) which is the difference betweenthe post-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value. Thesearch vector generator unit 20#A then calculates the interpolation bitestimation value based on the approximate value of each bit D_(i) ^((k))for the digital value and calculates the search vector δ_(i) ^((k))based on that difference.

The correction direction for the weighting coefficient of each bit isdetermined by the search vector δ_(i) ^((k)), and the weightingcoefficient can be converged to an optimum value so as to reduce theerror signal e(k) by the coefficient search unit 50 by utilizing the LMSalgorithm.

The A/D converter circuit 1#A can therefore execute high-speed andhigh-accurate A/D conversion processing based on the first embodiment.

In comparison to the example of the related art, the above structure ornamely the AD converter circuit 1#A based on the first embodiment has asimple structure including a single A/D converter unit (ADC), and alsorequiring no mechanism for applying an offset so that along with asmaller surface area, an increase in consumption current can also beprevented.

(First Modification of the First Embodiment)

[Formula 9]

Examining the properties of the binomial coefficient shows that formula(25) can express the power of (1−z⁻¹). First of all, formula (25) can bewritten as shown below utilizing z conversion.

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}^{\prime}\lbrack {\sum\limits_{l = 0}^{2\; n}{{Z^{- 1}( {- 1} )}_{n}^{n - l}C_{l}z^{- l}Z\;{x(k)}}} \rbrack} \times \lbrack {\sum\limits_{l = 0}^{2\; n}{{Z^{- 1}( {- 1} )}_{n}^{n - l}C_{l}z^{- l}Z\; D_{i}^{(k)}}} \rbrack}}} & (26)\end{matrix}$

Here, Z denotes z conversion and Z⁻¹ denotes inverse z conversion. Theproperties of the binomial coefficient yield:

$\begin{matrix}{{\sum\limits_{l = 0}^{m}{{{}_{}^{}{}_{}^{}}a^{l}b^{n - 1}}} = ( {a + b} )^{m}} & (27)\end{matrix}$

so that by setting a=1, b=−z⁻¹, and m=2n we obtain,

$\begin{matrix}{{\sum\limits_{l = 0}^{2\; n}{( {- 1} )_{n}^{n - l}C_{l}}} = ( {1 - z^{- 1}} )^{2\; N}} & (28)\end{matrix}$

Therefore, formula (26) can be rewritten as follows.W _(i) ^((new)) =W _(i) ^((old))−μ′_(i) [Z ⁻¹(1−z ⁻¹)^(2n) Zx(k)]×[Z⁻¹(1−z ⁻¹)^(2n) ZD _(i) ^((k)])  (29)

At this point, (1−z⁻¹) in formula (29) is a transfer function whosehigh-pass characteristic has a maximum value and frequencycharacteristics such that the amplitude is that of a Nyquist frequency.

The weighting coefficient search formula on the other hand is notrestricted to a form that is a power of (1−z⁻¹), and is capable ofsearching the weighting coefficient even if the (1−z⁻¹) in formula (29)is substituted with a typical high-pass characteristic transfer functionH(z).

Consider the case for example where the transfer function H(z) isassumed to be an FIR (Finite Impulse Response) filter.

$\begin{matrix}{\;\lbrack {{Formula}\mspace{14mu} 10} \rbrack} & \; \\{{e(k)} = {{Z^{- 1}{H(z)}Z\;{x(k)}} = {{\sum\limits_{m}{h_{m}{x( {k - m} )}}} = {\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )}}}} & (30)\end{matrix}$

When utilizing the above formula, the search vector δ_(i) ^((k)) is:

$\begin{matrix}{\delta_{i}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{i}} = {{\frac{\partial\;}{\partial W_{i}}\lbrack {Z^{- 1}{H(z)}Z\;{x(k)}} \rbrack} = {{\frac{\partial\;}{\partial W_{i}}{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )}} = {\sum\limits_{m}{h_{m}D_{i}^{({k - m})}}}}}}} & (31)\end{matrix}$

Therefore, the weighting coefficient search formula is:

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \lbrack {\sum\limits_{m}{h_{m}D_{i}^{({k - m})}}} \rbrack}}} & (32)\end{matrix}$

Or if correcting formula (32) to a formula for H(z) is:W _(i) ^((new)) =W _(i) ^((old))−μ′_(i) [Z ⁻¹ H(z)Zx(k)]×[Z ⁻¹ H(z)ZD_(i) ^((k))]  (33)

However, the transfer function for the search vector generator unit anderror signal generator unit need not always be the same so bysubstituting with H₁(z) and H₂(z) to distinguish between both, we canwrite the weighting coefficient search formula as:W _(i) ^((new)) =W _(i) ^((old))−μ′_(i) [Z ⁻¹ H ₁(z)Zx(k)]×[Z ⁻¹ H₂(z)ZD _(i) ^((k))]  (34)and this formula is more generally used than the weighting coefficientsearch formula mentioned above.

The structural diagram for the case when utilizing the search formula offormula (34) is described next.

FIG. 10 is a drawing for describing the structure of A/D convertercircuit 1#B based on a first modification of the first embodiment.

FIG. 10 shows the case where utilizing a digital filter 252 for thetransfer function H₁(Z) as the search vector generator unit 20.

FIG. 10 also shows the case where utilizing a digital filter 452 for thetransfer function H₂(z) as the error signal generator unit 40.

Here, assuming that the transfer function H(z) derived in the abovedescribed formula (33) is FIR, a transfer function H(z) that is IIRmight not always be established with formula (33).

However, the weighting coefficient can be calculated by formula (34)even when the transfer function H(z) is IIR.

The above described structure is capable of utilizing a digital filteras the search vector generator unit 20 and the error signal generatorunit 40.

(Second Modification of the First Embodiment)

When the signal band on the other hand, is on the low frequency side,the error signal generator unit 40 can generate an error signalutilizing a high-pass filter as the digital filter. Conversely, when thesignal band is, on the high frequency side, the error signal generatorunit 40 can generate an error signal utilizing a low-pass filter as thedigital filter. However offset correction is required.

Offset correction is required because the offset is equivalent to noisein the low frequency component and so correctly searching for thecoefficient requires canceling out the offset by way of an offsetcorrection. When the A/D conversion circuit is designed, the digitalvalue output from the A/D conversion circuit will not always be zeroeven for the case of zero input. The voltage potential from this zero iscalled the offset.

A second modification of the first embodiment is described for the casewhere correcting the offset.

FIG. 11 is an outline diagram for describing the structure of A/Dconverter circuit 1#C based on a second modification of the firstembodiment.

The A/D converter circuit 1#C as shown in FIG. 11, differs from the A/Dconverter circuit 1 in FIG. 1 in the point that the A/D convertercircuit 1#C further contains an offset corrector unit 60 to correct theoffset in the output value from the digital corrector unit 30.

The specific structure of the offset corrector unit 60 is describednext.

[Formula 11]

Adding an offset correction term W_(OFS) to the digital output valuefrom the ADC gives:

$\begin{matrix}{{x(k)} = {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}} + W_{OFS}}} & (35)\end{matrix}$

Assuming the H(z) is FIR and substituting in gives.

$\begin{matrix}{{e(k)} = {{Z^{- 1}{H(z)}Z\;{x(k)}} = {{\sum\limits_{m}{h_{m}{x( {k - m} )}}} = {{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )} + {\sum\limits_{m}{h_{m}W_{OFS}}}}}}} & (36)\end{matrix}$

The offset correction term first of all is:

$\begin{matrix}{\frac{\partial{e(k)}}{\partial W_{OFS}} = {{\frac{\partial\;}{\partial W_{OFS}}\lbrack {Z^{- 1}{H(z)}Z\;{x(k)}} \rbrack} = {{{\frac{\partial\;}{\partial W_{OFS}}{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )}} + {\frac{\partial\;}{\partial W_{OFS}}{\sum\limits_{m}{h_{m}W_{OFS}}}}} = {{\sum\limits_{m}h_{m}} \propto 1}}}} & (37)\end{matrix}$

The search formula for the offset correction term is therefore providedin the following formula.

$\begin{matrix}{W_{OFS}^{({new})} = {W_{OFS}^{({old})} - {\mu_{OFS}{\sum\limits_{m}{h_{m}{x( {k - m} )}}}}}} & (38)\end{matrix}$

Rewriting the above formula to an expression utilizing H(z) gives thefollowing formula.W _(OFS) ^((new)) =W _(OFS) ^((old))−μ_(OFS) Z ⁻¹ H(z)Zx(k)  (39)

FIG. 12 is a drawing for describing the circuit structure of A/Dconverter circuit 1#C based on a second modification of the firstembodiment.

As shown in FIG. 12, the present example shows the case where a digitalfilter 252 for the transfer function H_(i)(z) is utilized as the searchvector generator unit 20, and a digital filter 452 for the transferfunction H₂(z) is utilized as the error signal generator unit 40.

An offset corrector unit 60 includes a multiplier 68 for the multiplyingfactor μ_(OFS) according to formula (39), a subtracter 66 to subtractthe output from the multiplier 68 from the pre-rewrite offset correctionterm W_(OFS), a retention unit 64 to output the output from thesubtracter 66 as the post-rewrite offset correction term W_(OFS), and anadder 62 to add the post-rewrite offset correction term W_(OFS), to theoutput of the digital corrector unit 30.

The weighting coefficient is the same as described above and so theweighting coefficient search formula is formula (32) or formula (33).

The above structure is capable of utilizing a low-pass filter as thedigital filter for the error signal generator unit 40 by offsetcorrection via the offset corrector unit 60.

(Third Modification of the First Embodiment)

The weighting coefficient search processing on the other hand causesconvergence of the weighting coefficient to an optimal value, howeverthe converged weighting coefficient does not always match with anoptimum value and fluctuations may possibly occur in the vicinity of theoptimal value, possibly causing deterioration in the characteristics ofthe A/D converter circuit.

A method for preventing deterioration in A/D converter circuitcharacteristics is described in a third modification of the firstembodiment. More specifically, removing weighting coefficientfluctuations by a digital filter is capable of preventing deteriorationin A/D converter circuit characteristics.

FIG. 13 is an outline diagram for describing the structure of the A/Dconverter circuit 1#D based on a third modification of the firstembodiment.

The A/D converter circuit 1#D shown in FIG. 13, differs from the A/Dconverter circuit 1 in FIG. 1 in the point that a digital filter 70 isfurther provided for filter processing of the weighting coefficientsoutput from the coefficient search unit 50.

The specific structure of the digital filter 70 is described next.

As one example, a FIR filter, an IIR filter, an adaptive filter, andother filters may be utilized as the digital filter 70.

FIG. 14 is a drawing for describing the circuit structure of A/Dconverter circuit 1#D based on a third modification of the firstembodiment.

As shown in FIG. 14, the present example shows the case where theweighting coefficient searching processing is performed by utilizing4-point interpolation based on formula (8) as described in FIG. 8. Morespecifically, the utilization of the search vector generator unit 20#and the error signal generator unit 40# is shown. The case where an IIRfilter 70 is provided as the digital filter 70 between the coefficientsearch unit 50 and the digital corrector unit 30 is shown.

FIG. 15 is a drawing for describing the IIR filter 70 circuit structurebased on a third modification of the first embodiment.

As shown in FIG. 15, the IIR filter 70 is comprised of plural delayelements 608 to delay the signal from the adder 602, plural multipliers606 for the filter constants b0 to bn, an adder 604 for adding theoutputs from the plural multiplier 606 for the filter constants b0 tobn, the plural multipliers 605 for the filter constants 1 a to 1 n, andan adder 602 to add the input signals and outputs from the pluralmultipliers 605 of the filter constants a1 to an.

The FIR filter is equivalent to a setting of filter constant a1 to an=0.

(Fourth Modification of the First Embodiment)

In the above description, the case is described where the error signalgenerator unit 40 calculates the error signal e(k) based on the digitalvalue x(k) output from the digital corrector unit 30. However thecalculation is not limited to the digital value x(k) output from thedigital corrector unit 30, and may also calculate the error signal e(k)by other formulas.

[Formula 12]

Examining formula (30) and formula (31) gives:

$\begin{matrix}{{e(k)} = {{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )} = {{\sum\limits_{i = 0}^{N - 1}( {W_{i}{\sum\limits_{m}{h_{m}D_{i}^{({k - m})}}}} )} = {\sum\limits_{i = 0}^{N - 1}{W_{i}\delta_{i}^{(k)}}}}}} & ( {39A} )\end{matrix}$So the error signal e(k) can be calculated from the search vector δ_(i)^((k)).

The structure in FIG. 1 can therefore be modified as shown next if basedon the formula (39A).

FIG. 16 is an outline diagram for describing the structure of the A/Dconverter circuit 1A based on a fourth modification of the firstembodiment.

Comparing to the A/D converter circuit 1, the A/D converter circuit 1Aas shown in FIG. 16, differs in the point that the error signalgenerator unit 40 is replaced by an error signal generator unit 45.

The error signal generator unit 45 is capable of calculating the errorsignal e(k) by multiplying the weighting coefficient W_(i) by the searchvector δ_(i) ^((k)) from the search vector generator unit 20 and summingthem, according to formula (39A).

In comparison to the related art, the structure of the A/D convertercircuit 1A based on a fourth modification of the first embodiment is asimple structure including a single A/D converter unit (ADC). Also, nomechanism for applying an offset is required so that along with asmaller surface area, an increase in consumption current can also beprevented. This structure can also be applied to other embodiments andmodifications.

Second Embodiment

In the second embodiment, an A/D converter circuit for executing timeinterleaving operation capable of high-speed processing is described.

(When there are 2 Time Interleavings)

FIG. 17A and FIG. 17B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit 2based on the second embodiment.

The A/D converter circuit 2 based on the second embodiment as shown inFIG. 17A, is comprised of the A/D converter units (ADC) 10-1, 10-2, thesearch vector generator units 20-1, 20-2, digital corrector units 30-1,30-2, the error signal generator units 40-1, 40-2, the coefficientsearch units 50-1, 50-2, and the output selector switch 75.

The A/D converter units 10-1, 10-2 convert the analog input signals intodigital values that are the AD conversion results.

The search vector generator units 20-1, 20-2 calculate the interpolationbit estimation value based on the approximate values for each D_(1.i)^((k)), D_(2.i) ^((k)) which are digital values respectively output fromthe A/D converter units 10-1, 10-2, and also calculate the respectivesearch vectors δ_(1.i) ^((k)), δ_(2.i) ^((k)) based on the difference.

The error signal generator units 40-1, 40-2 calculate the digital valuesx₁(k), x₂(k) respectively output from the digital corrector units 30-1,30-2, and calculate the error signals e₁(k), e₂(k) based on theinterpolation estimation value based on the approximate values.

The coefficient search units 50-1, 50-2 provided to respectivelycorrespond to the digital corrector units 30-1, 30-2, search theweighting coefficients W_(1.i), W_(2.i) for each bit based on the searchvector δ_(1.i) ^((k)), δ_(2.i) ^((k)) output respectively from thesearch vector generator units 20-1, 20-2 and the error signals e₁(k),e₂(k) output from the error signal generator unit 40-1, 40-2.

The digital corrector units 30-1, 30-2 provided to respectivelycorrespond to the A/D converter units 10-1, 10-2, perform digitalcorrection of each bit D_(1.i) ^((k)), D_(2.i) ^((k)) for correspondingdigital values from A/D converter units 10-1, 10-2 according to theweighting coefficients W_(1.i), W_(2.i) for each bit that is searched bythe coefficient search units 50-1, 50-2. More specifically, the digitalcorrector units 30-1, 30-2 calculate the digital values x₁(k), x₂(k) bymultiplying the weighting coefficients W_(1.i), W_(2.i) by the digitalvalues for each bit D_(1.i) ^((k)), D_(2.i) ^((k)) from the A/Dconverter units 10-1, 10-2 and summing them.

The output selector switch 75 respectively switches and outputs thedigital values x₁(k), x₂(k) output from the digital corrector units30-1, 30-2 according to the clocks φ₁, φ₂.

A concept drawing of the conversion timing for the A/D converter,circuit 2 is shown here while referring to FIG. 17B. The present exampleshows the case where alternately and repeatedly implementing sampling(“S”) as one example of sampling processing of an analog input signal,and AD conversion (“AD”) for processing the sampled analog input signalby A/D conversion.

In the time interleaving operation, the clocks for processing areoperated after shifting the phase of the clocks φ₁, φ₂. The presentexample shows the case where there are two time interleavings, and thephase of the clocks φ₁, φ₂ are shifted a half cycle. Sampling processingis performed during the pulse rise of the clocks φ₁, φ₂. This operationoutputs digital values respectively from the A/D converter units 10-1,10-2, and the digital values after digital correction are alternatelyoutput by way of the output selector switch 75 to allow high-speed A/Dconversion processing.

(When there are 4 Time Interleavings)

FIG. 18A and FIG. 18B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit 2Abased on the second embodiment.

The A/D converter circuit 2A based on the second embodiment as shown inFIG. 18A is comprised of the A/D converter units (ADC) 10-1 to 10-4,search vector signal generator units 20-1 to 20-4, digital correctorunits 30-1 to 30-4, error signal generator units 40-1 to 40-4,coefficient, search units 50-1 to 50-4, and an output selector switch76.

The A/D converter units 10-1 to 10-4 convert the analog input signalsinto digital values that are the AD conversion results.

The search vector generator units 20-1 to 20-4 calculate theinterpolation bit estimation value based on the approximate value ofeach bit D_(1.i) ^((k)) to D_(4.i) ^((k)) in the digital valuesrespectively output from the A/D converter units 10-1 to 10-4 andrespectively calculate the search vectors δ_(1.i) ^((k)) to δ_(4.i)^((k)) based on the difference.

The error signal generator units 40-1 to 40-4 calculate the errorsignals e₁(k) to e₄(k) based on the interpolation estimation valuesbased on the approximate valves, and the digital values x₁(k) and x₄(k)respectively output from the digital corrector units 30-1 to 30-4.

The coefficient search units 50-1 to 50-4 search the weightingcoefficients W_(1.i) to W_(4.i) for each bit based on the search vectorsδ_(1.i) ^((k)) to δ_(4.i) ^((k)) that are respectively output from thesearch vector generator units 20-1 to 20-4 and the error signals e₁(k)to e₄(k) that are output from the error signal generator units 40-1 to40-4.

The digital corrector units 30-1 to 30-4 respectively digitally correcteach bit D_(1.i) ^((k)) to D_(4.i) ^((k)) of the digital value, from theA/D converter units 10-1 to 10-4 according to the weighting coefficientsW_(1.i) to W_(1.i) of each bit searched by the coefficient search units50-1 to 50-4. More specifically, the digital corrector, units 30-1 to30-4 calculate the digital values x₁(k) to x₄(k) by multiplying theweighting coefficients W_(1.i) to W_(4.i) by each bit D_(1.i) ^((k)) toD_(4.i) ^((k)) of the digital values output from the A/D converter units10-1 to 10-4 and summing them.

The output selector switch 76 selectively outputs the digital valuesx₁(k) to x₄(k) output from the digital corrector units 30-1 to 30-4according to the clocks φ₁ to φ₄.

An outline diagram of the conversion timing for the A/D convertercircuit 2A is shown here while referring to FIG. 18B. The presentexample shows the case where alternately and repeatedly implementingsampling (“S”) as one example of sampling processing of an analog inputsignal, and implementing AD conversion (“AD”) for processing the sampledanalog input signal by A/D conversion.

In the time interleaving operation, the clocks for processing areoperated by shifting the phase of the clocks φ₁, φ₂, φ₃, φ₄. The presentexample shows the case where there are four time interleavings and thephase of the clocks φ₁, φ₂, φ₃, φ₄ are shifted a quarter cycle. Samplingprocessing is performed during the pulse rise of the clocks φ₁, φ₂, φ₃,φ₄. This operation outputs the digital values respectively from the A/Dconverter units 10-1 to 10-4, and the digital values after digitalcorrection are alternately output by way of the output selector switch76 to allow high-speed A/D conversion processing.

(When there are n Number of Time Interleavings)

FIG. 19A and FIG. 19B are an outline diagram and a conversion timingdrawing for describing the structure of the A/D converter circuit 2Bbased on the second embodiment.

The A/D converter circuit 2B based on the second embodiment as shown inFIG. 19A is comprised of the A/D converter units (ADC) 10-1 to 10-n,search vector generator units 20-1 to 20-n, digital corrector units 30-1to 30-n, error signal generator units 40-1 to 40-n, coefficient searchunit 50-1 to 50-n, and an output selector switch 77.

The A/D, converter units 10-1 to 10-n convert the analog input signalsinto digital values that are the AD conversion results.

The search vector generator units 20-1 to 20-n calculate theinterpolation bit estimation values based on the approximate value foreach bit D_(1.i) ^((k)) to D_(n.i) ^((k)) for the digital valuesrespectively output from the A/D converter units 10-1 to 10-n, andrespectively calculate the search vectors δ_(1.i) ^((k)) to δ_(n.i)^((k)) based on the difference.

The error signal generator units 40-1 to 40-n calculate the errorsignals e₁(k) to e₄(k) based on the digital values x₁(k) and x_(n)(k)respectively output from the digital corrector units 30-1 to 30-n andthe interpolation estimation values based on the approximate valves.

The coefficient search units 50-1 to 50-n search the weightingcoefficients W_(1.i) to W_(n.i) for each bit based on the search vectorsδ_(1.i) ^((k)) to δ_(n.i) ^((k)) respectively output from the searchvector signal generator units 20-1 to 20-n and the error signals e₁(k),e_(n)(k) output from the error signal generator units 40-1 to 40-n.

The digital corrector units 30-1 to 30-n perform digital correction ofdigital values for each bit D_(1.i) ^((k)) to D_(n.i) ^((k))corresponding to the A/D converter units 10-1 to 10-n according to theweighting coefficients W_(1.i) to W_(n.i) for each bit that is searchedby the coefficient search units 50-1 to 50-n of each A/D converter units10-1 to 10-n. More specifically, the digital corrector units 30-1 to30-n calculate the digital values x₁(k) to x₂(k) by multiplying theweighting coefficients W_(1.i) to W_(n.i) by the digital value for eachD_(1.i) ^((k)) to D_(1.i) ^((k)) from the A/D converter units 10-1 to10-n and summing them.

The output selector switch 77 respectively selects and outputs thedigital values x₁(k) to x_(n)(k) output from the digital corrector units30-1 to 30-n according to the clocks φ₁ to φ_(n).

An outline diagram of the conversion timing for the A/D convertercircuit 2A is shown here while referring to FIG. 19B. The presentexample shows the case where alternately and repeatedly implementingsampling (“S”) as one example of sampling processing of an analog inputsignal, and implementing AD conversion (“AD”) to convert the sampledanalog input signal.

In the time interleaving operation, the clocks for processing areoperated by shifting the phase of the clocks φ₁, φ₂, . . . φ_(n). Thepresent example shows the case where there are four time interleavingsand the phase of the clocks φ₁, φ₂, . . . φ_(n) are shifted a quartercycle. Sampling is performed during the pulse rise of the clocks φ₁, φ₂,. . . φ_(n). This operation outputs the digital values respectively fromthe A/D converter units 10-1 to 10-n, and the digital values afterdigital correction are alternately output by way of the output selectorswitch 77 to allow high-speed A/D conversion processing.

(First Modification of the Second Embodiment)

In the modification of the second embodiment, an A/D converter circuitfor executing time interleaving operation capable of reducing thesurface area-along with high-speed processing is described next.

(When there are 2 Time Interleavings)

FIG. 20 is an outline diagram for describing the structure of the A/Dconverter circuit 2C based on a first modification of the secondembodiment.

The A/D converter circuit 2C based on the modification of the secondembodiment as shown in FIG. 20 differs from the A/D converter circuit 2of FIG. 17 in the point that the error signal generator units 40-1, 40-2are integrated into one error signal generator unit 40.

The error signal generator unit 40 calculates the error signal e(k)based on the digital value x(k) output from the output selector switch75 and the interpolation estimation value based on the approximate valueand outputs them to the coefficient search units 50-1, 50-2.

On the other hand, there is the possibility that spurious frequenciesmight occur due to the occurrence of offset mismatches among timeinterleave channels due to switching of the post-correction digitalvalue x(k) input to the error signal generator unit 40 from the outputselector switch 75 according to the clocks φ₁, φ₂. These spuriousfrequencies may cause deterioration in the A/D converter circuitcharacteristics.

An offset mismatch corrector unit 90 to correct the offset mismatch anda coefficient search unit 50Q to search the coefficients for correctingthe target offset mismatch are therefore further provided.

The coefficient search unit 50Q searches the coefficient W_(1.OFS) thatare utilized for offset correction in the offset mismatch corrector unit90 based on the error signal e(k) which is the output from the errorsignal generator unit 40.

The post-correction digital value is expressed here as shown in thefollowing formula.

$\begin{matrix}\lbrack {{Formula}\mspace{14mu} 13} \rbrack & \; \\{{x(k)} = {{\sum\limits_{i = 0}^{N - 1}{\gamma_{l}^{(k)}W_{l,i}D_{i}^{(k)}}} + {\gamma_{l}^{(k)}W_{l,{OFS}}}}} & (40)\end{matrix}$is expressed as shown above. The meaning of each variable is givenbelow.

L: denotes an index expressing a channel

Y^(L) ^((k)) : denotes a coefficient expressing on which channel the ADconversion of the k-th sample is performed

W_(L.1): denotes a weighting coefficient for channel

W_(L.OFS): denotes an offset correction term for channel L

k: denotes an index for expressing the number of the sample

x(k): denotes the digital output value obtained by AD conversion of thek-th sample

D_(i) ^((k)): denotes the i-th bit of the AD conversion results for thek-th sample

Here, Y^(L) ^((k)) =+1 when the k-th sample is AD converted by the ADCof channel L, and Y^(L) ^((k)) =0 in all other cases. Assuming that H(z)is FIR, the error signal is given below as:

$\begin{matrix}{{e(k)} = {{Z^{- 1}{H(z)}Z\;{x(k)}} = {{\sum\limits_{m}{h_{m}{x( {k - m} )}}} = {{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{\gamma_{l}^{({k - m})}W_{l,i}D_{i}^{({k - m})}}}} )} + {\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}W_{l,{OFS}}} )}}}}} & (41)\end{matrix}$At this time the search vector δ_(L.i) ^((k)) is given as follows:

$\begin{matrix}{\delta_{l,i}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{l,i}} = {{\frac{\partial\;}{\partial W_{l,i}}\lbrack {Z^{- 1}{H(z)}Z\;{x(k)}} \rbrack} = {{{\frac{\partial\;}{\partial W_{l,i}}{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{\gamma_{l}^{({k - m})}W_{l,i}D_{i}^{({k - m})}}}} )}} + {\frac{\partial}{\partial W_{l,i}}{\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}W_{l,{OFS}}} )}}} = {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}D_{i}^{({k - m})}}}}}}} & (42)\end{matrix}$Therefore, the search formula for the weighting coefficient is:

$\begin{matrix}{W_{l,i}^{({new})} = {W_{l,i}^{({old})} - {{\mu_{l,i}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \lbrack {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}D_{i}^{({k - m})}}} \rbrack}}} & (43)\end{matrix}$and can also be derived for the offset correction term with the samesearch formula. First of all,

$\begin{matrix}{\frac{\partial{e(k)}}{\partial W_{l,{OFS}}} = {{\frac{\partial\;}{\partial W_{l,{OFS}}}\lbrack {Z^{- 1}{H(z)}Z\;{x(k)}} \rbrack} = {{{\frac{\partial\;}{\partial W_{l,{OFS}}}{\sum\limits_{m}( {h_{m}{\sum\limits_{i = 0}^{N - 1}{\gamma_{l}^{({k - m})}W_{l,i}D_{i}^{({k - m})}}}} )}} + {\frac{\partial\;}{\partial W_{l,{OFS}}}{\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}W_{l,{OFS}}} )}}} = {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}}}}}} & (44)\end{matrix}$and therefore the search formula for the offset correction term is asfollows.

$\begin{matrix}{W_{l,{OFS}}^{({new})} = {W_{l,{OFS}}^{({old})} - {{\mu_{l,{OFS}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \lbrack {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}}} \rbrack}}} & (45)\end{matrix}$

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch in offsetsbetween time interleaving channels.

The above structure further allows reducing the number of parts andreducing the surface area by using one error signal generator unit, andwithout requiring the usage of two error signal generator units.

(When there are 4 Time Interleavings)

FIG. 21 is an outline diagram for describing the structure of the A/Dconverter circuit 2D based on a first modification of the secondembodiment.

The A/D converter circuit 2D based on a first modification of the secondembodiment as shown in FIG. 21 differs from the A/D converter circuit 2Aof FIG. 18 in the point that the error signal generator units 40-1 to40-4 are integrated into one error signal generator unit 40.

The error signal generator unit 40 calculates the error signal e(k)based on the digital value x(k) output from the output selector switch76 according to the clocks φ₁ to φ₄ and the interpolation estimationvalue based on the approximate value, and outputs them to thecoefficient search units 50-1 to 50-4.

The A/D converter circuit 2D further includes an offset mismatchcorrector unit 90 to correct an offset mismatch, and a coefficientsearch unit 50Q to search coefficients to correct the offset mismatch.

The coefficient search unit 50Q searches the coefficient W_(1.OFS) thatis utilized for offset correction in the offset mismatch corrector unit90 based on the error signal e(k) which is the output from the errorsignal generator unit 40.

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch amongoffsets in time interleaving channels.

The above structure further allows reducing the number of parts andreducing the surface area by integrating the error signal generatorunits into one error signal generator unit, without requiring theproviding of four error signal generator units.

(When there are n Number of Time Interleavings)

FIG. 22 is a drawing for describing the structure of the A/D convertercircuit 2E based on the first modification of the second embodiment.

The A/D converter circuit 2E based on the first modification of thesecond embodiment as shown in FIG. 22 differs from the A/D convertercircuit 2B of FIG. 19 in the point that the error signal generator units40-1 to 40-n are integrated into one error signal generator unit 40.

The error signal generator unit 40 calculates the error signal e(k)based on the digital value x(k) from the output selector switch 77according to the clocks φ₁ to φ_(n) and the interpolation estimationvalue based on the approximate value, and outputs them to thecoefficient search units 50-1 to 50-n.

An offset mismatch corrector unit 90 to correct the offset mismatch anda coefficient search unit 50Q to search the coefficients for correctingthe target offset mismatch are further provided.

The coefficient search unit 50Q searches the coefficient W_(1.OFS) thatare utilized in the offset mismatch corrector unit 90 based on the errorsignal e(k) which is the output from the error signal generator unit 40.

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch amongoffsets in time interleaving channels.

The above structure further allows reducing the number of parts andreducing the surface area by using one error signal generator unit, andwithout requiring the usage of n number of error signal generator units.

(Second Modification of the Second Embodiment)

FIG. 23 is a drawing for describing the A/D converter circuit 3 based ona second modification of the second embodiment.

FIG. 23 shows here the case where plural (2 units) samplers (S/H) areprovided.

The two sampler (S/H) units are capable of retaining the analog inputsignals at respectively different timings according to the clocks φ₁, φ₂and respectively outputting them.

Mismatches may occur such as in the gain and offset among channels fortime interleaving due to switching of the plural samplers (S/H) output,and spurious frequencies might possibly occur. These mismatches andspurious frequencies might sometimes cause deterioration in the A/Dconverter circuit characteristics.

A method to prevent the above deterioration in the A/D converter circuitcharacteristics in the A/D converter circuit 3 based on the secondmodification of the second embodiment is described next.

Specifically, the A/D converter circuit 3 further includes a gainmismatch corrector unit 80 for correcting the gain mismatch, an offsetmismatch corrector unit 90 to correct the offset mismatch, an interleaveimage generator unit 85, and coefficient search units 502, 50Q.

The interleave image generator unit 85 generates the interleave imageδ_(1.Gain) ^((k)) based on the post-correction digital value x′(k) thatis corrected in the digital corrector unit 30 according to the formula(48) described later on. The interleave image δ_(1.Gain) ^((k))generated in this way is a signal containing the same frequencycomponents as the spurious frequencies generated by the mismatch ingain.

The coefficient search unit 502 searches the coefficient W_(1.gain) thatis utilized for correcting the gain in the gain mismatch corrector unit80 based on the interleave image δ_(1.Gain) ^((k)) that is output fromthe interleave image generator unit 85 and the error signal e(k) whichis the output from the error signal generator unit 40.

The coefficient search unit 50Q searches the coefficient W_(1.OFS) thatis utilized for correcting the offset in the offset mismatch correctorunit 90 based on the error signal e(k) that is the output from the errorsignal generator unit 40. The offset correction term is the same asdescribed in formula (45).

The gain correction is described next.

[Formula 14]

Here, Y^(L) ^((k)) =+1 when the k-th sample is sampled by the S/H ofchannel i, and Y^(L) ^((k)) °=0 in all other cases. The digital outputvalue of the ADC is expressed as:

$\begin{matrix}{{x(k)} = {{( {1 + {\gamma_{l}^{(k)}W_{l,{Gain}}}} ){\sum\limits_{i = 0}^{N - 1}{W_{l}D_{i}^{(k)}}}} + {\gamma_{l}^{(k)}W_{l,{OFS}}}}} & (46)\end{matrix}$

The meaning of each variable is given below.

L: denotes an index expressing a channel

Y^(L) ^((k)) : denotes a coefficient expressing on which channel the ADconversion of the k-th sample is performed

W_(i): denotes a weighting coefficient

W_(1.OFS): denotes an offset correction term for channel L

W_(1.Gain): denotes the gain correction coefficient for channel L

k: denotes an index for expressing the number of the sample

x(k): denotes the digital output value obtained by AD conversion of thek-th sample

D_(i) ^((k)): denotes the i-th bit of the AD conversion results for thek-th sample

Assuming that H(z) is FIR, the error signal is given below as:

$\begin{matrix}{{e(k)} = {{Z^{- 1}{H(z)}Z\;{x(k)}} = {{\sum\limits_{m}{h_{m}{x( {k - m} )}}} = {{\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} \rbrack} + {\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}W_{l,{OFS}}} )}}}}} & (47)\end{matrix}$

The interleave image δ_(1.Gain) ^((k)) at this time is:

$\begin{matrix}\begin{matrix}{\delta_{l,{Gain}}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{l,{Gain}}} = {\frac{\partial}{\partial W_{l,{Gain}}}\lbrack {Z^{- 1}{H(z)}{{Zx}(k)}} \rbrack}}} \\{= {{\frac{\partial}{\partial W_{l,{Gain}}}{\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} \rbrack}} +}} \\{\frac{\partial}{\partial W_{l,{Gain}}}{\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}W_{l,{OFS}}} )}} \\{= {\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )}} \\{= {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}{x^{\prime}( {k - m} )}}}}\end{matrix} & (48)\end{matrix}$However, a substitution is made:

$\begin{matrix}{{x^{\prime}(k)} = {\sum\limits_{i = 0}^{N - 1}W_{i}D_{i}^{(k)}}} & ( {48A} )\end{matrix}$So that the search formula for the gain correction coefficient is givenbelow as:

$\begin{matrix}\begin{matrix}{W_{l,{Gain}}^{({new})} = {W_{l,{Gain}}^{({old})} - {{\mu_{l,{Gain}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \lbrack {\sum\limits_{m}{h_{m}{x^{\prime}( {k - m} )}}} \rbrack}}} \\{= {W_{l,{Gain}}^{({old})} - {{\mu_{l,{Gain}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times}}} \\{\lbrack {\sum\limits_{m}( {h_{m}\gamma_{l}^{({k - m})}{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}}} )} \rbrack}\end{matrix} & (49)\end{matrix}$The search formula for the weighting coefficient is derived the same asin formula (32) however applying the gain correction coefficient givesthe following formula.

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \{ {\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )}D_{i}^{({k - m})}} \rbrack} \}}}} & (50)\end{matrix}$

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch in offsetand gain.

FIG. 24 is a drawing for describing the A/D converter circuit 3A basedon a second modification of the second embodiment.

The structure as shown in FIG. 24 contains n number of samplers.

The n number of samplers (S/H) are capable of retaining the analog inputsignals at respectively different timings according to the clocks φ₁ toφ_(n) and respectively outputting them.

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch in offsetsand gain according to the same methods as already described.

FIG. 25 is a drawing for describing the A/D converter circuit 3B basedon a second modification of the second embodiment.

Compared to the A/D converter circuit 3A in FIG. 24, the A/D convertercircuit 3B as shown in FIG. 25 shows the case where the mountingsequence for the gain mismatch corrector unit 80 and the offset mismatchcorrector unit 90 are interchanged.

The offset correction and the gain correction in this case are shown bythe following formula.

[Formula 15]

Expressed as given below:

$\begin{matrix}{{x(k)} = {( {1 + {\gamma_{l}^{(k)}W_{l,{Gain}}}} ) \times ( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}} + {\gamma_{l}^{(k)}W_{l,{OFS}}}} )}} & (51)\end{matrix}$Assuming that H(z) is FIR, the error signal is given below as:

$\begin{matrix}\begin{matrix}{{e(k)} = {Z^{- 1}{H(z)}{{Zx}(k)}}} \\{= {\sum\limits_{m}{h_{m}{x( {k - m} )}}}} \\{= {\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )} \times ( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}} + {\gamma_{l}^{({k - m})}W_{l,{OFS}}}} )} \rbrack}}\end{matrix} & (52)\end{matrix}$The interleave image δ_(1.Gain) ^((k)) is at this time given as follows:

$\begin{matrix}\begin{matrix}{\delta_{l,{Gain}}^{(k)} = {\frac{\partial{e(k)}}{\partial W_{l,{Gain}}} = {\frac{\partial}{\partial W_{l,{Gain}}}\lbrack {Z^{- 1}{H(z)}{{Zx}(k)}} \rbrack}}} \\{= {\frac{\partial}{\partial W_{l,{Gain}}}{\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )} \times} }}} \\ ( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}} + {\gamma_{l}^{({k - m})}W_{l,{OFS}}}} ) \rbrack \\{= {\sum\limits_{m}\lbrack {h_{m}{\gamma_{l}^{({k - m})}( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}} + {\gamma_{l}^{({k - m})}W_{l,{OFS}}}} )}} \rbrack}} \\{= {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}{x^{''}( {k - m} )}}}}\end{matrix} & (53)\end{matrix}$However, a substitution is made as follows:

$\begin{matrix}{{x^{''}(k)} = {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{(k)}}} + {\gamma_{l}^{(k)}W_{i,{OFS}}}}} & ( {53A} )\end{matrix}$Therefore, the search formula for the gain correction coefficient isgiven as:

$\begin{matrix}\begin{matrix}{W_{l,{Gain}}^{({new})} = {W_{l,{Gain}}^{({old})} - {{\mu_{l,{Gain}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \lbrack {\sum\limits_{m}{h_{m}\gamma_{l}^{({k - m})}{x^{''}( {k - m} )}}} \rbrack}}} \\{= {W_{l,{Gain}}^{({old})} - {{\mu_{l,{Gain}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times}}} \\{\{ {\sum\limits_{m}\lbrack {h_{m}{\gamma_{l}^{({k - m})}( {{\sum\limits_{i = 0}^{N - 1}{W_{i}D_{i}^{({k - m})}}} + {\gamma_{l}^{({k - m})}W_{l,{OFS}}}} )}} \rbrack} \}}\end{matrix} & (54)\end{matrix}$The search formula for the weighting coefficient is derived the same asin formula (32), however a gain correction coefficient is applied sothat:

$\begin{matrix}{W_{i}^{({new})} = {W_{i}^{({old})} - {{\mu_{i}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \{ {\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )}D_{l}^{({k - m})}} \rbrack} \}}}} & (55)\end{matrix}$is obtained. The offset correction term is the same as the casedescribed above however a gain correction coefficient is applied whichgives the following formula.

$\begin{matrix}{W_{l,{OFS}}^{({new})} = {W_{l,{OFS}}^{({old})} - {{\mu_{l,{OFS}}\lbrack {\sum\limits_{m}{h_{m}{x( {k - m} )}}} \rbrack} \times \{ {\sum\limits_{m}\lbrack {{h_{m}( {1 + {\gamma_{l}^{({k - m})}W_{l,{Gain}}}} )}\gamma_{l}^{({k - m})}} \rbrack} \}}}} & (56)\end{matrix}$

The above structure is capable of preventing deterioration in A/Dconverter circuit characteristics by correcting the mismatch in offsetsand gain according to the same method as described above.

Third Embodiment

In the A/D converter circuits of the first and second embodiments,structures capable of background operation are described, however thesignal waveform of the analog input signal that is input to the A/Dconverter unit 10 might not always operate normally during searchprocessing for the weighting coefficient.

For example, if there is no change in the analog input signal, theconversion results from the A/D converter circuit are fixed so that theerror signal is always 0. There is no rewrite of the weightingcoefficient at this time so that the search processing for the weightingcoefficient does, not function. In other words, this task does notoperate correctly.

Therefore, the case where inputting a signal separate from the analoginput signal in advance, in order to execute the search processing forthe weighting coefficient and executing the foreground operation tosearch the weighting coefficient is described.

FIG. 26A and FIG. 26B are drawings for describing the signal input tothe A/D converter unit 10 based on the third embodiment.

Referring to FIG. 26, the present example describes the structure thatincludes a test signal generator circuit 6 to generate a test signal,and further includes a switch SW to switch the analog input signal andthe test signal from the test signal generator circuit 6. The switch SWreceives the analog input signal and the test signal, and switches thesignal for input to the A/D converter unit 10 by switching by the switchSW.

Here, FIG. 26A shows here the case where executing search processing forthe weighting coefficient (during the weighting coefficient searchoperation). More specifically, the test signal generator circuit 6 andthe A/D converter unit 10 are coupled by the switch SW. The coefficientsearch unit 50 in this way implements the search processing for theweighting coefficient by way of a test signal from the test signalgenerator circuit 6 and the search converges on the appropriateweighting coefficient.

Next, FIG. 26B shows the case where implementing A/D conversionoperation (during A/D conversion operation). More specifically, theanalog input signal and the A/D converter unit 10 are coupled by theswitch SW. In the present example, the coefficient search unit 50converges the weighting coefficient by search processing of theweighting coefficients by way of the test signal from the test signalgenerator circuit 6 so that the A/D conversion operation by the analoginput signal can achieve high-accuracy A/D conversion operation based onthe converged weighting coefficients.

FIG. 27 is a circuit structural diagram of the test signal generatingcircuit 6 based on the third embodiment.

The test signal generator circuit 6 shown in FIG. 27 is comprised ofresistors R1 to R3, operational amplifiers CP1, CP2, and a condenser C.

The operational amplifier CP1 outputs the amplified results of thedifference in voltage between the input of the node N3 and the clampingvoltage to the node NO. The resistor R2 is mounted between the node N3and the node NO. The resistor R3 is mounted between the node NO and thenode N1. The operational amplifier CP2 outputs the amplified results ofthe difference in voltage between the input of the node N1 and theclamping voltage to the node N2. The condenser C is mounted between thenode N1 and the node N2. The resister R1 is mounted between the node N2and the node N3. The structure of the present example is capable ofoutputting a triangular wave signal from the node N2.

In the present example, the case where utilizing a triangular wavesignal as the test signal is described, however the present invention isnot limited in particular to a triangular wave signal and signals of asine wave or a random wave may also be utilized as the test signal.

In the above processing the test signal generator circuit 6 generates atest signal assumed beforehand in the third embodiment, and executingthe search processing for the weighting coefficients according to thetest signal guarantees the capability to securely implement the searchoperation for the weighting coefficients so that a high-speed,high-accuracy A/D converter circuit can be achieved.

Fourth Embodiment

In the description for the above embodiment, a structure is employed inwhich the results from analog-digital (AD) conversion are input directlyto the digital corrector unit and coefficient search unit to implementsearch processing for the weighting coefficient.

The fourth embodiment is described for the case where executing thesearch processing for the weighting coefficient by another method.

FIG. 28 is an outline diagram for describing the structure of the A/Dconverter circuit 4 based on the fourth embodiment.

In comparison to the A/D converter circuit 1, the A/D converter circuit4 shown in FIG. 28 differs in the point that along with including astorage device 7, the digital corrector units′30P and 30Q are providedinstead of the digital corrector unit 30. Other points are the same asdescribed in FIG. 1 so a redundant, detailed description of identicalpoints is omitted.

More specifically, the output from the A/D converter unit 10 is input tothe storage device 7. The storage device 7 then retains the ADconversion results from the A/D converter unit 10 as data sequences.

The storage device 7 is capable of a simulated output of A/D conversionresults output from the A/D, converter unit 10 by reproducing(outputting) the retained data sequences to the digital corrector unit,etc.

In the present example, the search processing of the weightingcoefficients is performed by utilizing the data sequences reproduced(output) by the storage device 7. Namely, the appropriate weightingcoefficient is searched according to the same processing as describedabove by using the search vector generator unit 20, the digitalcorrector unit 30Q, the coefficient search unit 50, and the error signalgenerator unit 40.

The coefficient search unit 50 then outputs the searched weightingcoefficients to the digital corrector unit 302. The digital correctorunit 30P digitally corrects the AD conversion results output from theA/D converter unit 10 by using the weighting coefficient output from thecoefficient search unit 50.

The above structure is capable of rendering a high-speed, high-accuracyA/D conversion circuit by searching the weighting coefficients byutilizing the data sequences retained in the storage device 7.

In the above structure, the digital corrector units 302 and 30Q canutilize respectively different speeds and timings for the operatingspeed.

The time for the weighting coefficient search for example can beshortened by operating the digital corrector unit 30Q at a higher speedthan the digital corrector unit 302. In this case, the storage device 7may repeatedly reproduce (output) the retained AD conversion resultsmultiple times.

Operating the digital corrector unit 30P at a higher speed than thedigital corrector unit 30Q allows reducing the consumption current inthe search operation for the weighting coefficient.

The digital corrector unit 30P and 30Q can also be jointly utilized bytime sharing. The above structure would allow operation with a singledigital corrector unit 30P.

The storage device 7 need not always store all of the AD conversionresults, and preferably stores data sequences capable of beingeffectively utilized during a search for weighting coefficients.

In regards to this point, the search processing for the weightingcoefficient might not always operate normally due to the signal waveformfor the analog input signal. For example, if there is no change in theanalog input signal, the conversion results from the A/D convertercircuit are fixed results so the error signal is always at 0. There isno rewrite of the weighting coefficient at this time so the weightingcoefficient search processing does not function. Therefore, when achange in the AD conversion results is detected, the data sequences maybe stored in the storage device 7.

FIG. 29 is a drawing for describing the converging of the error signalsbased on the fourth embodiment.

Referring to FIG. 29A, in this example the sampling frequency forsearching the weighting coefficients of both the A/D converter unit 10and the coefficient search unit 50 are 10 MHz.

Referring to FIG. 29B, in this example the sampling frequency of the A/Dconverter unit 10 is set to 10 MHz, and for the coefficient search unit50 the search operation for weighting coefficient is set to 100 MHzwhich is 10 times the sampling frequency in FIG. 29A. In contrast to theerror signal convergence requiring approximately 100 μs in FIG. 29A, theerror signal convergence in FIG. 29B requires only approximately 10 μswhich allows confirming the high-speed processing is achieved.

Fifth Embodiment

A specific example of a product (semiconductor integrated circuit)capable of applying the above described A/D converter circuit isdescribed in the fifth embodiment.

FIG. 30 is a drawing for describing the structure of the wirelessreceiver 100 based on the fifth embodiment.

As shown in FIG. 30, the wireless receiver 100 is comprised of anantenna 102, a frontend module 104, an LNA (Low Noise Amplifier) 106, amixer 108, an oscillator circuit 110, a PGA (Programmable GainAmplifier) 112, a LPF (Low-pass filter) 114, an A/D converter circuit 1,a digital filter 116, and a demodulator unit 118.

The A/D converter circuit 1 is comprised of an A/D converter unit 10, asearch vector generator unit 20, a digital corrector unit 30, an errorsignal generator unit 40, and a coefficient search unit 50.

The frontend module 104 outputs the RF signal (wireless signal) that isreceived at the antenna 102 to the LNA 106. The LNA 106 appropriatelyamplifies the signal according to the band. The oscillator circuit 110generates a local (LO) oscillator signal. The mixer 108 frequencyconverts the RF signal into a baseband signal by multiplying the local(LO) oscillator signal. The PGA 112 then amplifies the baseband signalto the desired signal level. The LPF 114 removes external bandinterference wave from the baseband signal. The A/D converter circuit 1then performs A/D conversion of the baseband signal from an analogsignal to a digital signal. More specifically, the A/D converter unit 10performs A/D conversion (AD conversion) of the baseband signal from ananalog signal to a digital signal. The digital corrector unit 30 thencalculates the digital output value x(k) by multiplying the weightingcoefficient W_(i) by each bit D_(i) ^((k)) in the AD conversion resultsoutput from the A/D converter unit 10 and summing them. The searchvector generator unit 20 generates the search vector δ_(i) ^((k))utilizing each bit D_(i) ^((k)) from the AD conversion results. Theerror signal generator unit 40 calculates the error signal e(k). Thecoefficient search unit 50 calculates the weighting coefficient W_(i)based on the search vector δ_(i) ^((k)) and the error signal e(k).

The digital filter 116 then removes any external band interference wavethat the LPF 114 has not already removed and quantization noise fromoutside the band generated in the AD conversion. The demodulator unit118 then reproduces the original signal.

The wireless receiver 100 is in other words capable of applying andutilizing the A/D converter circuit 1 based on the present embodiment.The A/D converter circuit 1 is described in the present example howeverA/D converter circuits based on other embodiments and modifications mayalso be applied.

(Modification of the Fifth Embodiment)

FIG. 31 is a drawing for describing the sensor 120 based on amodification of the fifth embodiment.

In FIG. 31, the sensor 120 is a Wheatstone bridge type sensor circuit.

The sensor 120 is comprised of a Wheatstone bridge circuit 122, an AFE(Analog Front End) 124, and an A/D converter circuit 1. The Wheatstonebridge circuit 122 includes resistors RT1 to RT4. The resistors RT1 toRT4 configure a Wheatstone bridge and a portion or all of the resistorsare sensor elements.

FIG. 32 is a drawing for describing the structure of the AFE 124 basedon a modification of the fifth embodiment.

FIG. 32 shows an instrumentation amplifier as one example of the AFE124. More specifically, the AFE 124 is comprised of resistors R10 toR16, and operational amplifiers CP3 to CP5.

The operational amplifier CP3 outputs the results from amplifying thedifference in voltage between the voltage Vp input and the node N6. Theresistor R10 is mounted between node N3 and node N6. The resistor R13 ismounted between the node N3 and the node N4.

The operational amplifier CP4 outputs the results from amplifying thedifference in voltage between the voltage Vn input and the node N7. Theresistor R11 is mounted between node N6 and node N7. The resistor R12 ismounted between node N7 and node N8. The resistor R15 is mounted betweennode N8 and node N9. The resistor R16 is mounted between node N9 and theclamping voltage. The operational amplifier. CP5 outputs the amplifiedresults of the difference in voltage between node N4 and node N9 to nodeN5. The resistor R14 is mounted between the node N4 and node N5.

In the Wheatstone bridge circuit 122, the voltage Vp=Vn when theresistance values of resistors RT1 through RT4 are equivalent. When aportion or all of the resistors RT1, RT2, RT3, and RT4, are sensorelements, a change in the physical quantity that is the target forobservation causes a fluctuation in a portion or all of resistancevalues of RT1 through RT4 and so generates a voltage across voltagesVp-Vn. Therefore, measuring the voltage across voltage Vp-Vn allowsmeasuring the change in physical quantity for the sensor element that isthe target for observation. The voltage across voltage Vp-Vn isgenerally tiny and so is amplified by AFE 124. The A/D converter circuit1 then performs AD conversion of the analog signal amplified by AFE 124into a digital signal. More specifically, the A/D converter unit 10performs AD conversion of the analog signal output from the AFE 124 to adigital signal. The digital corrector unit 30 then calculates thedigital output value x(k) by multiplying the weighting coefficient W_(i)by each bit D_(i) ^((k)) in the AD conversion results output from theA/D converter unit 10 and summing them. Moreover, the search vectorgenerator unit 20 generates the search vector δ_(i) ^((k)) by utilizingeach bit D_(i) ^((k)) from the AD conversion results. The error signalgenerator unit 40 calculates the error signal e(k). The coefficientsearch unit 50 then calculates the weighting coefficient W_(i) based onthe search vector and the error signal e(k).

Namely, the sensor 120 is capable of applying and utilizing the A/Dconverter circuit 1 based on the present embodiment. The A/D convertercircuit 1 is described in the present example however A/D convertercircuits based on other embodiments and modifications may also beapplied.

The number of sensor elements utilized to configure the structure in thesensor 120 varies. The sensor element is an element whose resistancevalue fluctuates according to some type of physical quantity and forexample a temperature sensor, magnetic sensor, optical sensor,acceleration sensor or other sensors may be mounted according to thephysical quantity that is the target for observation and the A/Dconversion circuit based on the present embodiment can be applied to anyof these sensors.

Sixth Embodiment

The sixth embodiment is described in a specific example utilizing theabove described A/D converter circuit.

According to the field of application, a multiplexer may in some casesbe mounted at the input to the A/D converter unit 10 to performanalog/digital (AD) conversion of multiple analog inputs in a single A/Dconverter unit 10.

A multiplexer for example may actually be mounted for example in amicrocontroller.

A large change occurs in the input to the A/D converter unit 10 at thispoint regardless of the input signal band of each input when themultiplexer input is switched.

However, when considering each input to the multiplexer, there arelimits on the input signal bandwidth at each input so high-speed A/Dconversion processing can be achieved by isolating the A/D conversionresults for each input.

FIG. 33 is an outline diagram for describing the structure of the A/Dconverter circuit 5 based on the sixth embodiment.

The A/D converter circuit 5 as shown in FIG. 33 is comprised of an A/Dconverter unit 10, multiplexers MP1 to MP3, search vector generatorunits 20-1 to 20-3, digital corrector units 30-1 to 30-3, error signalgenerator units 40-1 to 40-3, and coefficient search units 50-1 to 50-3.

The multiplexer MP1 selectively accepts an input from the plural inputpaths of the inputs I1 to I3 and outputs it to the A/D converter unit 10according to the commands CT1 to CT3. When the command CT1 for exampleis input, the multiplexer MP1 accepts an input I1 and outputs it to theA/D converter unit 10. Also, when the command CT2 is input, themultiplexer MP1 accepts the input 12 and outputs it to the A/D converterunit 10. When the command CT3 is input, the multiplexer MP1 accepts theinput 13 and outputs it to the AD converter unit 10.

The demultiplexer MP2 selectively outputs the outputs from the A/Dconverter unit 10 along the plural output paths of the digital correctorunits 30-1 to 30-3 according to the commands. CT1 to CT3. When thecommand CT1 for example is input, the demultiplexer MP2 outputs thedigital value for input I1 from the A/D converter unit 10 to the digitalcorrector unit 30-1. When the command CT2 is input, the demultiplexerMP2 outputs the digital value for input I2 from the A/D converter unit10 to the digital corrector unit 30-2. When the command CT3 is input,the demultiplexer MP2 outputs the digital value for input 13 from theA/D converter unit 10 to the digital converter unit 30-3.

The multiplexer MP3 selectively accepts and outputs digital valuesoutput from the digital corrector units 30-1 to 30-3 according to thecommands CT1 to CT3. When the command CT1 for example is input, themultiplexer MP3 outputs a post-correction digital value for the input I1from the digital corrector unit 30-1. When the command CT2 is input, themultiplexer MP3 outputs a post-correction digital value for the input I2from the digital corrector unit 30-2. Also, when the command CT3 isinput, the multiplexer MP3 outputs a post-correction digital value forthe input I3 from the digital corrector unit 30-3.

The structure for the A/D converter unit 10, the search vector generatorunits 20-1 to 20-3, the digital corrector units 30-1 to 30-3, the errorsignal generator units 40-1 to 40-3, and the coefficient search units50-1 to 50-3 are identical to the description of the structure for thefirst embodiment so a detailed, redundant description is omitted.

FIG. 34 is an outline diagram for describing the structure of the A/Dconverter circuit 5A based on the sixth embodiment.

The A/D converter circuit 5A shown in FIG. 34 is comprised of an A/Dconverter unit 10, multiplexers MP1 to MPn, search vector generatorunits 20-1 to 20-n, digital corrector units 30-1 to 30-n, error signalgenerator units 40-1 to 40-n, and coefficient search units 50-1 to 50-n.

The multiplexer MP1 selectively accepts an input from the inputs I1 toIn and outputs it to the A/D converter unit 10 according to the commandsCT1 to CTn.

The demultiplexer MP2 selectively outputs an output from the A/Dconverter unit 10 to the digital corrector units 30-1 to 30-n accordingto the commands CT1 to CTn.

The multiplexer MP3 accepts and outputs the digital values output fromthe digital corrector units 30-1 to 30-n according to the commands CT1to CTn.

The structure for the A/D converter unit 10, the search vector generatorunits 20-1 to 20-n, the digital corrector units 30-1 to 30-n, the errorsignal generator units 40-1 to 40-n, and the coefficient search units50-1 to 50-n are identical to the description for the first embodimentso a detailed, redundant description is omitted.

The above structure allows achieving high-speed A/D conversionprocessing by isolating the A/D conversion results for each input.

(Modification of the Sixth Embodiment)

The above sixth embodiment describes a structure where the coefficientsearch units 50 are equal to the number of multiplexer inputs. Weightingcoefficient values different from each of the multiplexer inputs areutilized.

The A/D converter unit 10 however is jointly utilized so the calculatedweighting coefficients are the same for any of the multiplexer inputs.

Therefore, installing one coefficient search unit 50 will provesufficient. A description of an A/D converter circuit capable of asmaller surface area is described for the modification of the sixthembodiment.

FIG. 35A and FIG. 35B are outline diagrams for describing the structureof the A/D converter circuit 5B and the coefficient search unit 50 basedon a modification of the sixth embodiment.

The A/D converter circuit 5B shown in FIG. 35A is comprised of an A/Dconverter unit 10, the multiplexers MP1, MP3, MP4, MP5, a demultiplexerMP2, the digital corrector units 30-1 to 30-3, the search vectorgenerator units 20-1 to 20-3, and the error signal generator units 40-1to 40-3.

The multiplexer MP1 selectively accepts the inputs I1 to I3 and outputs,them to the A/D converter unit 10 according to the commands CT1 to CT3.

The demultiplexer MP2 selectively outputs the output from the A/Dconverter unit 10 to the digital corrector units 30-1 to 30-3 accordingto the commands CT1 to CT3.

The multiplexer MP3 selectively accepts and outputs the digital valuesoutput from the digital corrector units 30-1 to 30-3 according to thecommands CT1 to CT3.

The coefficient search unit 50 for searching the weighting coefficientsis described while referring to FIG. 35B.

The multiplexer MP4 selectively accepts search vectors output from thesearch vector generator units 20-1 to 20-3 and outputs them to thecoefficient search unit 50.

The multiplexer MP5 selectively accepts error signals output from theerror signal generator units 40-1 to 40-3 and outputs them to thecoefficient search unit 50.

The structure for the A/D converter unit 10, the search vector generatorunits 20-1 to 20-3, the digital corrector units 30-1 to 30-3, the errorsignal, generator units 40-1 to 40-3, and the coefficient search unit 50are identical to the description of the structure for the firstembodiment so a detailed, redundant description is omitted.

The above structure allows mounting and jointly utilizing coefficientsearch unit 50 and so is capable of reducing the number of parts andreducing the surface area.

FIG. 36A and FIG. 36B are outline diagrams for describing the structureof the A/D converter circuit 5C based on a modification of the sixthembodiment.

The A/D converter circuit 5C shown in FIG. 36A is comprised of an A/Dconverter unit 10, the multiplexers MP1, MP3, MP4, MP5, a demultiplexerMP2, the digital corrector units 30-1 to 30-n, the search vectorgenerator units 20-1 to 20-n, and the error signal generator units 40-1to 40-n.

The multiplexer MP1 selectively accepts plural inputs from the pluralinput paths of the inputs I1 to In and outputs them to the A/D converterunit 10 according to the commands CT1 to CTn.

The demultiplexer MP2 selectively outputs the output from the A/Dconverter unit 10 to plural output paths of the digital corrector units30-1 to 30-n according to the commands CT1 to CTn.

The multiplexer MP3 selectively accepts and outputs the digital valuesoutput from the digital corrector units 30-1 to 30-n according to thecommands CT1 to CTn.

The coefficient search unit 50 for searching the weighting coefficientsis described while referring to FIG. 36B.

The multiplexer MP4 selectively accepts the search vectors output fromthe search vector generator units 20-1 to 20-n and outputs them to thecoefficient search unit 50 according to the commands CT1 to CTn.

The multiplexer MP5 selectively accepts error signals output from theerror signal generator units 40-1 to 40-n and outputs them to thecoefficient search unit 50 according to the commands CT1 to CTn.

The structure for the A/D converter unit 10, the search vector generatorunits 20-1 to 20-n, the digital corrector units 30-1 to 30-3, the errorsignal generator units 40-1 to 40-n, and the coefficient search unit 50are identical to the description of the structure for the firstembodiment so a detailed, redundant description is omitted.

The above structure allows mounting and jointly utilizing a coefficientsearch unit 50 and so is capable of reducing the number of parts andreducing the surface area.

The present invention rendered by the present inventors is describedbased on the embodiments however the present invention is not limited tothe embodiments and may include all manner of modifications andvariations not departing from the spirit and scope of the invention.

What is claimed is:
 1. An analog-to-digital converter circuit thatconverts an analog input signal into a digital quantity comprising: ananalog-to-digital converter unit that converts the analog input signalinto a pre-correction digital value; and a corrector unit that digitallycorrects the pre-correction digital value output from theanalog-to-digital converter unit, wherein the corrector unit includes: aweighting coefficient multiplier unit that outputs a post-correctiondigital value obtained by multiplying weighting coefficients providedfor each bit by each bit of the pre-correction digital value output fromthe analog-to-digital converter unit and summing them, and a weightingcoefficient search unit that searches for weighting coefficients so asto minimize an error signal generated based on the post-correctiondigital value and an approximate value for the post-correction digitalvalue.
 2. The analog-to-digital converter circuit according to claim 1,wherein the weighting coefficient search unit rewrites the weightingcoefficient provided for each bit by multiplying and summing the errorsignal by a search vector utilized for searching the weightingcoefficient which is generated based on each bit of the correspondingpre-correction digital value and the approximate value for each bit ofthe pre-correction digital value.
 3. The analog-to-digital convertercircuit according to claim 2, wherein the corrector unit furtherincludes: a search vector generator unit that generates search vectorsbased on each bit of the pre-correction digital value and theapproximate value of each bit of the pre-correction digital value, andan error signal generator unit that calculates the error signals basedon the post-correction digital value and the approximate value of thepost-correction digital value.
 4. The analog-to-digital convertercircuit according to claim 3, wherein the error signal generator unitcalculates the error signal as the difference between thepost-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value, andthe search vector generator unit generates the search vector based onthe difference between each bit of the pre-correction digital value andthe interpolation bit estimation value based on the approximate value ofeach bit of the pre-correction digital value.
 5. The analog-to-digitalconverter circuit according to claim 3, wherein the search vectorgenerator unit and the error signal generator unit are digital filters.6. The analog-to-digital converter circuit according to claim 1, whereinthe corrector unit further includes an offset corrector unit to performoffset correction on the output from the weighting coefficientmultiplier unit.
 7. The analog-to-digital converter circuit according toclaim 1, further comprising: a test signal generator circuit thatgenerates a desired test signal, and a switching circuit that switchesbetween the analog input signal and the test signal, and inputs theanalog input signal or the test signal into the analog-to-digitalconverter unit.
 8. The analog-to-digital converter circuit according toclaim 7, wherein the test signal is a triangular wave.
 9. Theanalog-to-digital converter circuit according to claim 7, wherein theweighting coefficient multiplier unit outputs a first post-correctiondigital value obtained by multiplying and summing the weightingcoefficients provided for each bit by the first pre-correction digitalvalue for each bit of the test signal output from the analog-to-digitalconverter unit, the weighting coefficient search unit searches forweighting coefficients so as to minimize an error signal generated basedon the first post-correction digital value and an approximate value forthe first post-correction digital value, and the weighting coefficientmultiplier unit outputs a second post-correction digital value obtainedby multiplying and summing the weighting coefficients searched by theweighting coefficient search unit by each bit of the secondpre-correction digital value for the analog input signal output from theanalog-to-digital converter unit during normal operation.
 10. Theanalog-to-digital converter circuit according to claim 1, furthercomprising: a plurality of samplers that are able to retain the analoginput signals at respectively different timings and outputting therespective analog input signals to the analog-to-digital converter unit,wherein the corrector unit further includes: a gain corrector unit thatcorrects mismatches in the gain among the channels generated byswitching the outputs from the samplers, and an offset corrector unitthat corrects mismatches in the offsets among the channels generated byswitching the outputs from the samplers.
 11. The analog-to-digitalconverter circuit according to claim 1, wherein the corrector unitfurther includes a digital filter mounted between the weightingcoefficient search unit and the weighting coefficient multiplier unit.12. A semiconductor integrated circuit comprising: an analog inputsignal generator unit that generates the analog input signals, and ananalog-to-digital converter circuit as described in the claim
 1. 13. Ananalog-to-digital converter circuit that converts an analog input signalinto a digital quantity comprising: a plurality of analog-to-digitalconverter units that convert the analog input signals intopre-correction digital values; and a corrector unit that digitallycorrects the pre-correction digital value output from theanalog-to-digital converter units, wherein the corrector unit includes:a plurality of weighting coefficient multiplier units that are mountedto correspond to each of the analog-to-digital converter units, andoutput a post-correction digital value obtained by multiplying aweighting coefficient for each bit by each bit in the correspondingpre-correction digital value and summing them; a plurality of weightingcoefficient search units that are mounted to correspond to each of theweighting coefficient multiplier units, and search a weightingcoefficient so as to minimize an error signal that is generated based onthe post-correction digital value and the approximate value of thepost-correction digital value, and an output selector unit thatrespectively switches and outputs the outputs from the weightingcoefficient multiplier units.
 14. The analog-to-digital convertercircuit according to claim 13, wherein each of the weighting coefficientsearch units rewrites the weighting coefficient provided for each bit bymultiplying and summing the error signal by a search vector utilized forsearching the weighting coefficient which is generated based on each bitof the corresponding pre-correction digital value and the approximatevalue for each bit of the pre-correction digital value.
 15. Theanalog-to-digital converter circuit according to claim 14, wherein thecorrector unit further includes: a plurality of search vector generatorunits that are mounted to correspond to each of the analog-to-digitalconverter units, and generates the search vectors based on each bit ofthe corresponding pre-correction digital value and the approximate valueof each bit of the pre-correction digital value; an offset correctorunit that performs offset correction on the output of each weightingcoefficient multiplier unit output from the output selector unit, and anerror signal generator unit that outputs the respective error signal tothe weighting coefficient search units based on the post-correctiondigital value output from the output selector unit and the approximatevalue of the post-correction digital value.
 16. The analog-to-digitalconverter circuit according to claim 15, wherein the error signalgenerator unit calculates an error signal as the difference between thepost-correction digital value and the interpolation estimation valuebased on the approximate value of the post-correction digital value, andeach of the search vector generator units generates the search vectorbased on the difference between each bit of the pre-correction digitalvalue and the interpolation bit estimation value based on theapproximate value of each bit of the pre-correction digital value.